Brick Lane in Shoreditch has been closed by firefighters working to put out a fire at an office block.
The second and third floor as well as the building's roof are alight and almost 60 firefighters are working to bring it under control.
One witness said the street has been cordoned off between Hanbury Street and Buxton Street. Emergency services were called just before 2.30pm.
Jamie Milestone, 33, a designer who works nearby, said he believes the four storey office block is empty.
He said: "I smelt the smoke and saw the fire, then the windows fell through. I think the offices have been empty for some time.
"They've shut the whole street and the fire seemed to be getting fiercer and there were lots of people standing around."
The Taste Brick Lane festival takes place today, with members of the public invited to sample food from one of the capital's most iconic streets.
The 2014 Taste Brick Lane awards will recognise the street's best curry house, and there will be entertainment on offer throughout the day including dancers, jugglers and henna artists.
The event begins at 12 noon today and goes on until 4pm.