People living near the site between East Hanningfield and Rettendon are being told to keep their windows and doors closed as footage shows a vast plume of black smoke and visible flames above the building.
Essex County Fire and Rescue Service also told people to "avoid the area if you can".
Colin Neale Jr was driving along the A13 near Dagenham when he saw the plumes of smoke.
He told Sky News that, as he drove closer, he realised how big the fire was and decided to send his drone up over the fields.
Mr Neale said the drone showed "multiple fields" had caught fire and it appeared two industrial complexes were affected.
A spokesman for East of England Ambulance Service said its hazardous area response team had gone to the scene.
Essex County Fire and Rescue Service area manager Dave Bond said: "The incident has been declared a major incident by the fire service due to the size of the fire that we're dealing with...
"There is still significant smoke... and we're advising people to stay away from the area while we deal with it.
"We do believe that we've got the fire surrounded now, but we ask for the public's patience while we extinguish the fire and bring the incident to a closure.
"We will provide further updates through our social media channels and our website, so please keep an eye on them for more information."
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Tony Bartlett, of Axminster, Devon, faces a minimum term of 18 years behind bars after attacking Atticus Bartlett on 16 July 2022 in a "sudden fit of anger".
The 39-year-old and his then-partner Evelyn Ballentyne, Atticus's mother, had gone to a pub and comedy club that evening, Bristol Crown Court previously heard.
Ms Ballentyne's mother, Rachel Donovan, and her husband Andrew went to the family home in Chard, Somerset, to care for the child.
Bartlett drank eight-and-a-half pints of lager over the course of the evening before returning home with Ms Ballentyne, and was left alone to feed Atticus in the living room, while she went upstairs to change around 11pm.
He then violently shook Atticus, it was alleged, causing severe internal injuries to the baby's brain and spinal cord.
Atticus' brain damage was so severe that he did not regain consciousness or manage to breathe for himself, and he died at Bristol Royal Hospital for Children just before midnight on 23 July 2022.
Bartlett was convicted of murder on 8 July after denying the charge and an alternative count of manslaughter.
Prosecuting, Charles Row KC said he had been "drunk and frustrated".
He told jurors: "Mr Bartlett can't admit to himself that when he was drunk, in a moment of pure violence, he did something that he will regret for the rest of his life."
The baby suffered three rib fractures which were not the result of resuscitation efforts.
Sentencing, Mr Justice Cavanagh told Bartlett: "I have no doubt that this terrible tragedy would not have happened if you were not so heavily intoxicated."
Bartlett had been feeding Atticus with a bottle and the baby was bringing up the milk.
The judge went on: "In your drunken state, Atticus's inability to take the bottle as well as you thought he should enraged you.
"You had a sudden fit of anger. You vented that anger on your tiny baby son. You shook him very violently indeed, gripping him very tightly round his ribcage.
"This only lasted a few seconds or at most a minute or so. Just in that brief moment, you wanted to cause Atticus serious injury."
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Experts said Atticus' injuries were associated with "vigorous shaking", with the fractures caused by "gripping and squeezing", the court heard.
Ms Ballentyne said she is contending with "severe anxiety" after her son's death.
She said in a victim personal statement: "I had to wait 11 hours and 18 minutes for Atticus to die. It was horrendous. I was scared to go out, I was scared to stay in.
"I don't enjoy any moments because I have a dead son. It is mentally and emotionally draining all the time. It is awful."
The 41-year-old said that while he had been "pretty sure" he was going to quit this summer when his previous team, the Los Angeles Lakers, exited the playoffs, he had now decided to give the sport one last shot.
James wrote on social media: "This is my last decision. I'm not going for money. I'm not going for family. What am I really playing for at this point?
"I still want to sacrifice. I still want to work. I still want to grind. I still want to compete, to win and to have a chance at the feeling of winning another championship."
He is the NBA's all-time leading scorer and has spent the last eight seasons of his career with the Lakers, leading them to a title win in 2020.
But the world of basketball has been on tenterhooks for weeks for news of his next move - and whether he would continue playing for a record-extending 24th season.
In a lengthy statement, James admitted: "I thought I was done when the season ended. I wasn't ready to announce it, and I knew I needed some time to really decide, but I was pretty sure I played my last game."
But he said the last few weeks had "really been special" while he took "real time to just think".
"I believe I can help make the Philadelphia 76ers a championship team and I am so excited to energise a new fan base and start this incredible journey one last time," James added.
However, commentators said the star may have his work cut out. The East Coast side has not won a title in 43 years.
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James did not disclose the terms of his new deal. But ESPN reported that the four-time champion had signed a two-year, $8m (£6m) contract.
Such a deal would be a significant pay cut, considering he reportedly made more than $50m (£37.5m) with the Lakers last season.
The vessel carrying armed officers hit the structure at around 3.40pm on Friday, according to the Metropolitan Police.
The Met said a number of officers "entered the water, but were recovered", following the crash that involved a boat from its marine policing unit.
Paramedics were seen treating the injured on a rigid black inflatable boat moored to the side of the River Thames.
The Met said in a statement: "We understand five officers were injured and are receiving treatment. We await an update on the extent of their injuries.
"At this stage, we don't believe any members of the public were involved or injured."
The Met said the circumstances of the incident will be "thoroughly reviewed, but at this stage our priority is the wellbeing of the officers involved".
A large number of police officers, fire crews and ambulances were on the scene - with traffic across the bridge overlooking the Houses of Parliament at a standstill.
A police boat was later seen being towed by a larger boat from the fire service.
Witnesses Katherine and Jim Bagley, from Gloucester in the US state of Massachusetts, were queuing for a river cruise when they saw an orange boat travelling at "high speed" along the river followed by the black police boat.
Mr Bagley told Sky News: "It looks to me that he [the police boat skipper] got stuck in the wake of the other boat that had just passed through the bridge and slammed into the wall on the opposite side...
"The next thing we saw was three people in the water, coming down the river."
While the couple did not see the moment of impact, Mr Bagley said the orange boat eventually turned around and came back to help.
He added: "Sadly, one of the men [in the water], from what we could tell, I don't know if he was unconscious or what, but he did not move the whole time we saw him there... I hope he's OK."
Cecilia Lusevic, 56, and her 12-year-old son Mateo Bilis-Lusevic said they heard a loud bang when the crash happened.
The visitors to the UK, from Chile, were on a Thames tour boat on the north side of the bridge. They were evacuated from their vessel shortly afterwards.
Mateo said: "Two boats were riding extremely fast through the water. Suddenly, I heard a boom. I was looking towards the boat, and I heard a boom.
"Then three people went flying into the water and one of the people was really hurt."
The officers were in the water for around 10 minutes and a life ring was thrown for one of them by someone, he said.
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Following the crash, crowds of onlookers watched the aftermath from the bridge before being moved from the area.
Surrounding roads and two entrances of nearby Westminster Underground station were also closed.
A Port of London Authority spokesperson said: "We are aware of an incident involving a police vessel at Westminster Bridge.
"We are supporting the response and providing assistance where needed, working closely with the Metropolitan Police, HM Coastguard and partner agencies to manage the situation."
Suspect Isobella Perrie Sullivan was granted bail after appearing before a special sitting of Trim District Court in Co Meath earlier this evening.
She was charged with possession of explosives.
Officers discovered the alleged bomb during an operation targeting "dissident republicans", Irish police said.
A police officer told the court that Ms Perrie Sullivan had been stopped on the N2 at Aclint, Carrickmacross, County Monaghan, about 6 miles (10km) from the border with Northern Ireland.
During a search of her vehicle, a bag was found in the rear seat which was found to contain Semtex and a detonator, the court heard.
Defence solicitor Gavin Booth said his client had been asked to take a bag to the north, and had not been aware what was in it.
On Friday, Irish police said the alleged car bomb, which officers said had the potential to cause "significant damage", had been intercepted on Wednesday afternoon. It is understood the device contained suspected military-grade explosives.
The woman and a man, aged in his 40s, were arrested on suspicion of offences against the state. The man remains in custody at a Garda station in the Dublin area.
Speaking earlier, Garda Commissioner Justin Kelly said police had made an "extremely significant seizure" and indicated the suspected bomb had already been constructed when it was seized.
"Unfortunately for operational reasons, I can't go into the exact detail of the device," he said.
"But what I will say, certainly it was a significant explosive device. So certainly not just the seizure of components or pieces.
"This was an explosive device and it would have or could have potentially caused significant damage."
Garda have described the alleged bomb as "highly sophisticated" and "advanced".
Garda requested the assistance of the Irish Defence Forces EOD (Explosive Ordnance Disposal) team to complete an examination of the vehicle.
'Radicalised republicans'
Commissioner Kelly said pulling over the car was "not a random stop" and had been an "intelligence-led operation".
He said there were still people who did not accept the peace treaty implemented under the Good Friday Agreement, which ended decades of sectarian conflict in Ireland, known as the Troubles.
"Any seizure of this nature is really concerning," he said.
"However, we certainly know that there are a small minority of dissident republicans who did not agree with the Good Friday Agreement, they did not put weapons and explosives [out of use], they didn't go through with the proper process in relation to decommissioning. So that is something that we continue to deal with.
"There's a small minority of these individuals, I would describe them as radicalised republicans, and this is a threat that we're going to continue to face for some time."
Police Service of Northern Ireland Assistant Chief Constable Davy Beck said police on both sides of the Irish border shared a "joint commitment" to tackle the dissident republican terror threat.
"This underlines our joint commitment to address the threat posed by violent dissident republican groups and keep communities safe," he said.
'Deeply concerning'
The discovery prompted concern from politicians in Ireland and the UK.
Northern Ireland Secretary Chris Bryant thanked the Irish national police and security service for their "quick, decisive action".
"Intercepting a dangerous device like this undoubtedly saved lives and kept communities safe on both sides of the border.
"Strong cross-border security cooperation remains as vital as ever," he said.
Deputy First Minister of Northern Ireland Emma Little-Pengelly said in a post on X that the incident is "deeply concerning".
Ireland's justice minister Jim O'Callaghan described the seizure as "very worrying".
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"I think it is very significant," he said. "I've been updated on that by the (Garda) Commissioner. I think it evidences the fact that there is an ongoing threat in respect of dissident republican activity."
He added: "The device has been, I suppose, procured for the gardaí and has been defused. So there's lots of issues in respect of it that are concerning. But I also want to commend the gardaí for the work they did in ensuring that this didn't become a real threat to the public."
Sporadic attacks by militant groups, often attempted car bombings, continue in Northern Ireland almost three decades after the 1998 peace deal largely brought sectarian violence in the British-run region to an end.