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The blaze broke out shortly after noon (1206GMT) in an industrial area in Stratford, authorities said. The fire is within the construction site for the 2012 Summer Olympics, the British Broadcasting Corp. reported.
About 75 firefighters from 15 fire engines were fighting the blaze, the London Fire Brigade said.
Extensive redevelopment is taking place in the area, about 9 kilometers (5.5 miles) east of central London.
Police said there was nothing to suggest a suspicious cause.
"We only know it's a fire," a Metropolitan Police spokeswoman said. "There's nothing to suggest anything else at the moment."
There were no reports of injuries. One railway line was closed because of smoke, Network Rail said.