Up to 150 houses and many cars were damaged when the freak weather hit the Kensal Rise area.

One man in his 50s suffered a serious head injury and five were treated for minor injuries and shock.

Fire services have sealed six roads in a zone covering a quarter of a square mile and searched at least 100 homes.

Fire crews were called at about 1100 GMT on Thursday to Chamberlayne Road and surrounding streets, amid reports of collapsed scaffolding and damage to buildings.

The emergency services sealed roads off

Witnesses said there was heavy rain and sleet, then debris flying through the air.

Resident Colin Brewer said: "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.

"I then saw clumps of all sorts of things flying into air. It went from exciting to terrifying."

Local resident Daniel Bidgood said: "I was in my living room and I heard a big crack of lightning and thunder, then as I went to the window I heard a sound which was like standing behind a jetliner.

"I could see a huge cloud rolling up the street, making this tremendous sound.

"I went to try to take a picture of it but a shower of debris smashed all the windows of my house."

He reported seeing trees ripped up from the roots, front doors missing, windows smashed and people being hit on the head by flying objects.

Dave Bonner, of London Fire Brigade, said one house had its roof completely removed while another had an exterior wall demolished.

Residents returning from work were told to report to the Church of the Transfiguration hall in Chamberlayne Road where they would be met by police and local authority representatives.

Brent Council has set up a respite centre at the nearby Legion Hall on Albert Road for residents who have been made temporarily homeless.

A council spokeswoman said about 70 people are at the hall but they are preparing to help about 150.

The UK experiences an estimated 50 tornadoes on land each year, putting it top of the European league.

'Not unusual'

The BBC Weather Centre said the tornado lasted less than minute.

"To see a tornado is not that unusual - but the magnitude of the damage due to the one in north-west London is," said BBC meteorologist Susan Powell.

She said the tornado formed due to a lot of energy in the air across the UK, producing widespread heavy thunderstorms with gusty winds.

"However, in the case of the shower in London, the massive up and down draughts came into phase, spiralling and forming a tornado," she said.

The Association of British Insurers said initial estimates suggested damage would be in the millions of pounds rather than tens of millions as seen in Birmingham tornado in 2005.

The last tornado which caused significant damage in London was in December 1954, in west London, in which six people were hurt and the roof of Gunnersbury London Underground station was ripped off.