About 100 houses were damaged and several hundred people forced to leave their homes in Kensal Rise district in the north-west of the capital by the 30-second twister, a police spokesman said.

At least one house had its side entirely pulled off and thrown into the street, according to television pictures.

"It was really, really incredible. All of a sudden I saw a swirl starting to form and then, it was amazing, but it then touched land," nearby resident Colin Brewer told BBC.

"I then saw clumps of all sorts of things flying into the air."

Some 20 fire trucks and 50 firefighters were rushed to the scene, while a local school was evacuated, said a fire service spokesman, adding that some people were being looked after in a local church hall.

Eyewitness James Miles told Sky News television that the sky went dark and there was thunder and lightning immediately before the tornado struck.

"Everything just goes round and round for about 20 seconds until it skips over you and then all of a sudden it's silent and then the debris is all over the place," he said.

Paramedics also rushed to the scene, and one man was taken to hospital with a head injury while five others were treated at the scene for minor injuries and shock, the capital's ambulance service said.

"I think a lot of people are shaken up because it's not the sort of thing that would happen in the centre of London," said Miles. "It's global warming I suppose, isn't it?" he added.

Another eyewitness, Sally Johnson, said she thought she was going to die. "All the cars and the windows, everything (was) smashed in," she told Sky. "There's debris everywhere, you can hardly walk."

The Association of British Insurers (ABI) said it was too early to estimate the cost of damage, but a spokesman recalled that a similar freak tornado which hit Birmingham last year caused tens of millions of pounds' worth of damage.

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