LONDON (Reuters) - London's tallest building, The Shard, was evacuated for several hours on Thursday after smoke started billowing from the basement of the 87-storey skyscraper, a fire brigade spokesman said.

The alarm was raised about 9.30am GMT and about 900 people were evacuated from the multi-purpose landmark tower while seven fire engines rushed to the scene.

By early afternoon, people were being allowed back in. "There was no fire in the building and all tenants and guests of the Shard are now re-entering," tweeted the management of The Shard.

A police spokesman said there were no reports of any injuries or arrests and investigations into the cause of the smoke were continuing.

The Shard, Western Europe's tallest skyscraper at about 310m, was funded by Qatar's royal family and opened in 2012. Its office space is about 50 per cent full.

The distinctive, elongated glass-clad pyramid was designed by architect Renzo Piano and has 72 habitable storeys housing a hotel and six companies including Qatar-based broadcaster Al Jazeera and the world's largest hospital group, Hospital Corporation of America.

Its top floors have become a tourist attraction in the capital, reserved for visitors who pay up to 30 pounds (S$63.20) to get a spectacular view of London.