Twenty firefighters were taken to hospital after tackling a massive blaze which ripped through industrial units in Essex.
Crews were called to Southend Road, between East Hanningfield and Rettendon, south of Chelmsford at 4.50pm on Friday and will remain into the weekend.
A major incident was declared and residents evacuated.
Chief fire officer Rick Hylton told a media conference on Saturday afternoon that three engines and two officer cars were destroyed in the aftermath.
Recounting the incident, he said: “Firefighters arrived quickly and were faced with a large and rapidly developing fire involving several units and surrounding farmland.”
A number of buildings and vehicles were gutted and a field caught alight after fertiliser inside one unit exploded – which people across the county reported hearing and seeing.
Witnesses said the sound was “like a bomb” before they saw a mushroom cloud that went up orange and yellow, then turned black. Others reported the ground shook and their windows rattled.
The fire service said more than 100 firefighters were working to tackle the blaze and nearby residents were evacuated for their own safety.
Mr Hylton added: “At 5.46pm, following an explosion involving fertiliser within one of the industrial units, Essex County Fire and Rescue Service declared a major incident.
“We took that decision because of the scale and complexity of the incident, the significant resources required to bring the fire under safe control, and the need to co-ordinate a multi-agency response.
“The fire and explosion has also destroyed three fire engines and two officer cars that were being used to respond to the incident. This underlines the scale and intensity of the conditions our crews faced.
“I also want to provide an update on the welfare of our firefighters. I can confirm that 20 firefighters attended hospital following the incident.
“Of that 20, four suffered minor injuries, and the remainder were precautionary assessments, including checks for issues such as hearing loss following the explosion.
“I am pleased to confirm all of those firefighters have now been discharged from hospital.”
A spokesman for East of England Ambulance Service said it had declared a critical incident and its hazardous area response team was in attendance.
Mr Hylton said: “Firefighters will remain at the scene in order to bring the incident to a safe resolution, a formal investigation into the cause of the incident has already begun.
“It is important that we do not speculate on the cause until that investigation has fully been completed.”
In a video update, Essex fire area manager Dave Bond added: “We’re still at the scene of a significant fire in East Hanningfield.
“As you can see behind me, we’re still dealing with significant spots of fire. However, we do have this incident under control and surrounded.
“We’re in the process of scaling back, but we do still have 50 firefighters on scene. We’re still working closely with our partners, including police, ambulance, utility companies, and we also have a number of specialist advisers on scene, giving us support as we move through the night.
“The incident will be ongoing into the weekend, so please stay away from the area and allow us to continue operations. We apologise for any inconvenience this caused, and we thank you for your patience.
“The advice we’re still giving to the public is that if you do smell smoke, then close your doors and windows. But please bear with us as we continue our operations to extinguish the fire.”
He added: “This is why we declared a major incident and I want to reassure our residents that there is no wider risk to the public at this time.
“Everybody at the scene is safe, residents nearby have been evacuated while we put the fire out and Southend Road is currently closed to allow us more space to work safely.
“Roads will remain closed, please avoid the area and thanks for your patience.”
Jackie Head, who lives close to the scene, said she saw smoke and then heard a “massive explosion” when she went to look at it.
“It was scary, everything shook, and people heard it for miles around,” she told BBC News.
“We had a bit of metal come through the air that was metres from us, which was beginning to set fire to the grass.
“My husband went over and kicked that out of the grass, but bits from the explosion set the back field alight.”
Her husband Phil Head added: “It was just mayhem, crazy. It happened within minutes.”
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