Four London Fire Brigade engines have been called to a blaze at Great Portland Street that created so much black smoke it could be seen through the windows of nearby live BBC studios.
The fire broke out in a lift motor room on the roof of a building undergoing refurbishment.
Heavy traffic built up in one of the busiest roads in central London.
The Brigade said they had the fire under control by 1.30 pm.
The fire was visible to Radio 2 presenter Jeremy Vine who could see it from his studio window.
By 12.30 LFB control room had taken thirty five 999 calls.