The fire broke out at a Shell-owned chemical plant on the same site as the Stanlow refinery in Ellesmere Port, Cheshire.
Essar Oil UK, which operates the refinery and chemical plant, say that 900 employees and 500 contractors work on the site which supplies 16% of all road transport fuels.
All staff have been accounted for and the fire has now been extinguished.
Flames and a column of thick black smoke were seen after the blaze broke out on Wednesday afternoon.
Large fire at ? Shell avoid the area
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Cheshire Fire Service, which was called at 2.16pm, said: “Firefighters have been called to reports of a fire at Stanlow oil refinery in Oil Site Road, Ellesmere Port.
“All staff have been accounted for and have been evacuated.
“Crews are working with onsite firefighters to extinguish the fire which is believed to be in a manufacturing building within the plant.”
We appear to have caught the on our CCTV!
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The force said the fire has been confined to the site and crews are using a ground monitor and handheld monitor to extinguish pockets of flame.
Brian Howell, 60, said he was relaxing in the Eastham Ferry area, around eight miles away, before he “heard a loud ‘whoosh‘ type explosion”.
He added: “I looked over to Stanlow and there was an aggressive fire and lots of black smoke.”
The Shell Higher Olefins Plant (SHOP) is separated from the refinery by a road and rail tracks.
We are aware of the fire at the Stanlow Oil Refinery in Elllesmere Port, and are working with to reduce any environmental impact.
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Essar said in a statement: “Earlier this afternoon a fire occurred at the SHOP chemical plant, close to the Manchester Ship Canal.
“Both Stanlow‘s own site Emergency Services Team and the Cheshire County Fire Service attended to deal with the incident. All personnel on the SHOP unit were quickly accounted for. The fire has now been extinguished.
“Operations and production of fuels and other products from Stanlow Refinery have not been affected.
“All supplies to customers are normal.”
The Stanlow refinery has a team of 25 full-time staff to allow for immediate action to prevent potential catastrophes.
Six fire engines attended the scene in Oil Site Road.
Stanlow produces 4.4 billion litres of diesel and three billion litres of petrol annually, according to Essar Oil UK.