The Jamaican prime minister, PJ Patterson, declared a state of emergency and pleaded with half a million people living in vulnerable areas to leave their homes as Hurricane Ivan raced towards the island last night.

"Residents living near coastal areas must evacuate before it's too late," Mr Patterson said in an address to the nation. "I cannot stress too strongly that Ivan is a dangerous hurricane. What we're experiencing now is only the beginning."

Seven-metre waves, thunderstorms and flooding preceded the eye of the hurricane, which was due to pass over Jamaica before heading to Cuba and Florida.

The government opened more than 1,000 emergency shelters, and urged the evacuation of 500,000 people in low-lying coastal communities, flood zones and shanty towns. But although the banks closed and shops ran out of basic supplies yesterday afternoon, few people made their way to the shelters, preferring to secure their roofs and wait at home.

Only about 1,200 people had moved into the shelters around Kingston, the emer gency management director, Barbara Carby, said, adding that people feared looting.

"I'm not saying I'm not afraid for my life, but we've got to stay here and protect our things," said Lorna Brown, 49, pointing to a stove, television, cooking utensils and large bed crowded into a one-room concrete home on the beach at Montego Bay.

Mrs Carby said that although there was concern about the ability of buildings to withstand 160mph winds, her greatest concern was the 3-5 metre (10-15ft) storm surges and flooding projected for coastal communities.

Last night, waves two-storeys high lashed the island's eastern shore, flooding homes and washing away roads.

Onlookers stood transfixed near Kingston's airport as 7 metre (23ft) waves crashed to shore, flinging rocks and tree branches more than 30 metres into the road.

"I've lived here all my life and I've never seen anything like this," said a businessman, Chester Pinnock. "This is going to be disastrous, we could have hundreds dead."

Last night the country was shut off from the outside world. Flights were cancelled and Air Jamaica parked its planes in the United States.

Hundreds of British holidaymakers were airlifted to the Dominican Republic for safety.

The Jamaican police went on emergency alert, fearing widespread looting, and a Royal Navy ship, HMS Richmond, sailed for the island to offer vital aid.

Ivan, the most destructive hurricane in the Caribbean for more than 10 years, has already killed 33 people.

The toll includes 22 in Grenada, including two unidentified foreigners from a yacht, one in Tobago, four in Venezuela, a Canadian woman in Barbados and four youngsters in the Dominican Republic, who were swept away by a giant wave even though the storm was 200 miles away.

Cuba declared a hurricane watch across the entire island. President Fidel Castro went on national television warning residents to brace themselves. "Whatever the hurricane does, we will all work together" to rebuild, he said.

Although it has caused havoc all over the Caribbean, its most deadly effects so far have been felt in Grenada, where the capital, St George's, was devastated.

Many prisoners escaped when the jail was damaged. Hundreds of looters smashed storm shutters and shop windows to take televisions and shopping trolleys of food. Some carried away bed frames and mattresses.

Ivan will be the third hurricane to pass through the area in a month, hammering both the Caribbean and Florida.

Three hurricanes closely following one another in one sea son is rare and there is still time for more this year.

This is exactly the sort of phenomenon that scientists on the Intergovernmental Panel on Climate Change fear may be the result of warmer sea temperatures - more violent and frequent storms.

Last year gave the South Atlantic its first hurricane, a surprise to meteorologists, and something many had thought would never happen.

In Florida, residents stopped clearing up the debris from hurricanes Charley and Frances to flee Ivan, pausing to join long queues once again at DIY stores and petrol stations.

"We've all been through this trilogy. It's no fun, but you do what you've got to do," Jane Fry told the Associated Press as she loaded supplies into her car.

There was still hope that the winds might veer west and hit the Gulf of Mexico. But if Ivan does land in Florida it could add to the death toll of 43 and the damage bill of $20bn (£11bn) in the past few weeks.