More than 30 firefighters have been tackling a barn fire involving 10 vehicles and thousands of litres of bio-fuel.
Crews were called to Trickley Coppice Farm at Middleton, in north Warwickshire, at about 2130 GMT on Wednesday, a spokesman said.
About 12,000 litres of bio-fuel are estimated to be on site, they added.
The barn is divided into five industrial units and used as a car and engineer workshop.
The cause is not yet known.