Scores of firefighters in Essex are tackling a blaze involving 160,000 litres of cooking oil.
They were alerted to the fire at a storage yard in Little Warley, near Brentwood, Essex, at 5.15am.
Assistant divisional officer Leigh Corke said 65 firefighters were dealing with the incident involving 160,000 litres of cooking oil, 30,000 tonnes of paper and 30,000 litres of diesel.
Crews from Brentwood, Orsett, Chelmsford, Basildon, Rayleigh Weir, Ingatestone, Ongar, Grays, Romford, Hornchurch and Harold Hill are taking part.
Utility companies and the Environment Agency have been called in by the fire service.
A fire service spokesman said: "Once the fire is out, a joint police and fire service investigation will be carried out to establish the cause."
He added that three hours into the blaze crews reported that 3,000 litres of diesel, 50,000 litres of cooking oil and other catering industry materials remain alight.
A water relay has been established and firefighters are using three jets, two foam branches and a ground monitor as they work to bring the incident under control.
Fifteen appliances are now dealing with the blaze, with fire crews from London drafted in to provide support.
Incident commander, divisional officer Mark Samuels, said he expected the flames to be extinguished by 11am.
He added: "Firefighters have been aggressively fighting the fire with foam. This is a recycling yard that recycles various types of used oils, hence the intensity of the fire.
"We are in the final stages of tackling the blaze, although we expect to be on the scene for several hours."