It is feared the storm may become a Category Five - the biggest of its type with winds of up to 150mph - and cause severe damage.

Dean is currently heading straight for Jamaica although the authorities in Haiti and neighbouring Dominican Republic as well as in the Cayman Islands and Mexico are also on standby.

It is feared that hundreds of British holidaymakers on the island could soon be caught up in the hurricane.

Andy Cooper, director general of the Federation of Tour Operators, said all FTO members' flights tomorrow to Mexico's Yucatan peninsula were cancelled. Planes will fly out empty and bring back tourists due home. A MyTravel flight destined for Jamaica tomorrow has also been delayed for 24 hours.

According to the FTO there are currently just under 4,000 Britons travelling with large tour operators in Jamaica, 9,000 in resorts in the Yucatan peninsula, and "literally a handful" in the Cayman Islands.

Cooper said: "It is our intention to leave customers there. They will go into shelters in accordance with local procedures."

The Foreign Office is advising against all non-essential travel to Jamaica, where both of the country's international airports are expected to close depending on prevailing weather conditions, the Jamaica Tourist Board said.

Basil Smith, the board's director of tourism, said: "It is expected that a Hurricane Watch phase will be implemented shortly," and the restrictions will remain "until further notice". But he added that no official evacuation has been ordered.

Meteorologists are already predicting an "unusually active" hurricane season and they have issued severe weather warnings for the whole region.

Jamaican prime minister Portia Simpson-Miller has ordered shelters to be opened across the island whilst calling for a halt to campaigning for the elections planned for later in the month.

She said: "Let us band together and unite in the threat of this hurricane."

The National Hurricane Centre in Miami said Dean could exceed 155 mph as it approaches the Gulf of Mexico tomorrow.

A spokesman added: "This storm is moving faster than the average storm.

"It is forecast to have a direct hit on Jamaica at a Category Four strength, which is an extremely dangerous storm."

Yesterday, Nasa ordered space shuttle Endeavour back to Earth a day early out of fear that Hurricane Dean might disrupt flight operations.