Smoke has been seen billowing into the sky over Canary Wharf after an air conditioning unit caught fire on top of the Barclays building.
Around 60 firefighters attended the scene after the London Fire Brigade were called out at 00.39 on Saturday.
The service received around 20 emergency calls during the blaze in the busy financial area in east London.
No injuries have been reported.
Eight fire engines from stations including Millwall and Shadwell were at the scene.
Twitter users posted images and video of the blaze at the 33-storey tower.
The fire was brought under control shortly before 2am.
Station manager Lee Sandy who was at the scene said: “While the fire was very visible, it was contained to the air conditioning unit on the roof of a commercial tower block.
“There were no people involved and the fire did not spread beyond the roof area.”