Four fire engines and 21 firefighters were called to a fire on a building site on Lanacre Avenue in Colindale this morning.
The fire affected a five storey building under construction and a tar boiler at roof level was destroyed in the blaze. One propane cylinder exploded before the Brigade arrived and a second propane cylinder was cooled by firefighters.
The Brigade was called at 1157 and the fire was under control by 1308. Crews from Hendon, Stanmore and Finchley fire stations are at the scene. The cause of the fire is under investigation.