The Queen and Duke of Edinburgh looked on in disbelief on Thursday as a whirlwind wreaked havoc at the third day of Royal Ascot.

The freak wind whisked a gazebo, chairs and ladies' hats a hundred feet into the air, sending punters scurrying for cover at the Berkshire course.

Two men were taken to hospital; one with a suspected heart attack, the other with cuts and bruises.

The Met Office at Bracknell recorded the Force 6 gust, describing it as a "dust devil".

All my young ladies' hats took off - people were screaming and hollering

Trevor Primett

The Royal couple had just arrived when the whirlwind struck.

The Queen watched from the Royal Box as picnic debris spiralled into the air.

Punter Trevor Primett, a businessman who brought 16 women to the royal races in a minibus, witnessed the whirlwind.

"All my young ladies' hats took off - people were screaming and hollering.

"There must have been thousands of paper plates and serviettes that shot skywards."

Mr Primett, 48, managing director of Basic Travel, in Hertford, said the gazebo landed in a bush, then took off again to land on the windscreen of a Jaguar car before being whisked away and landing among limousines in a Royal Ascot car park.

A Met Office spokesman said: "On days like this, hot air rises and, with cool air rushing in, an effect is created that spins the air."

Weather forecaster Michael Dukes said dust devils were quite common in Britain, although more often associated with the deserts of north Africa and Australia.