More than 200 firefighters are tackling a blaze which is said to be the biggest in London for several years.
Forty fire engines have been sent to the incident at a recycling centre on Chequers Lane in Dagenham, east London, about eight miles from the Olympic Park.
London Fire Commissioner Ron Dobson said: “We've not seen a fire of this size in London for several years. It's certainly a dramatic end to the Olympics for the London Fire Brigade.
“That said though, we are still able to attend incidents across the capital and the fire cover we're providing at the Olympic venues has not been affected.
“We've got over 200 firefighters from across London working hard under challenging conditions to bring the incident to a close. Fortunately, we've not had any reports of injuries at this stage.”
He added: “At this stage we aren't sure how the blaze started as our focus is getting the flames under control.”
London Fire Brigade said a plume of smoke could be seen across London at the height of the incident.
A single storey recycling building, which is around 50 metres by 100 metres, was completely alight.
Firefighters were called at 1.15pm and crews from Dagenham, Barking, East Ham and surrounding stations were sent to the scene. The cause of the fire is not known at this stage.
A spokesman for Locog said there was no indication that tonight's closing ceremony at the Olympic Stadium would be affected.
“Everything is going on as planned,” he added.