A man is being treated for burns after he was blown off an oil tank as it exploded and burst into flames at a Kent engineering company.
The blast involved tanks of used oil
Witnesses reported seeing huge flames rising into the air at the height of the blaze at the Kingsnorth Industrial Estate on the Hoo peninsula.
Nine staff were on the premises at the time of the blast but there were no other injuries.
The injured man was taken to the Medway Maritime Hospital with minor injuries.
Police said the industrial estate and businesses in the area were evacuated and an exclusion zone put in place around the scene of the fire.
Householders living around the site were told to stay indoors with the windows closed as a precautionary measure.
Ch Insp Peter Wedlake, of Kent Police, said the smoke was unpleasant to breathe in, but it was not dangerous.
Although crews remained at the scene, the blaze had been brought under control by mid-afternoon.
Roads surrounding the area were later reopened and the cordon scaled down.
Nine staff were on the premises at the time
Kent Fire and Rescue said the explosion had involved three tanks - one water tank and two tanks containing used engine oil.
Each is about 16ft (4.8m) in diameter and height.
Spokesman Bill Feeley said when firefighters arrived at the scene they found 200,000 litres of heavy oil alight.
"What we were dealing with was a massive chip pan - the whole surface area of the oil inside the tank was on fire and heating the metal tank," he said.
The fire service said one oil tank had ruptured, but had been surrounded by a barrier to stop the oil from spreading while the second tank was being cooled.
BBC South East news reporter Simon Jones, who is at the scene, said at the height of the blaze a huge amount of smoke from the incident had formed a blanket over the whole area.
Local resident, Sam Kitto, said she thought a plane had crashed when she heard the explosion.
"I felt the ground moving as well," she added.
At least 15 fire appliances and support vehicles were sent to the scene.
The Environment Agency said water used to put out the fire had contaminated a 300m (984ft) stretch of the water course.
A further 150,000 litres (33,000 gallons) of contaminated water had been contained on site.
Officers would be working over the weekend to clean up the area and avoid any further pollution.
The cause of the explosion is not yet known.