SHANGHAI, Aug. 14 (Xinhua) -- Firefighters have extinguished a fire at the top of the construction site of the planned tallest building in the Chinese mainland an hour after it broke out and no casualties were reported, according to the Shanghai municipal public security bureau.

The fire broke out at around 4:30 p.m. on Tuesday at an elevator shaft construction site on the 40th floor of the Shanghai World Financial Center in the city's Pudong New District.

The fire was put out at 5:45 p.m. with no casualties reported, the bureau said.

The building has a planned height of 492 meters, and already exceeds 420 meters.

An initial investigation showed the fire was caused by welding activities.

Construction of the 101-storey building began in November 2005.It is expected to be the tallest building in the Chinese mainland.