The deadly storm packed winds of up to 240 kilometers (150 miles) per hour as it headed for Jamaica where the authorities ordered the population to rush to take emergency precautions before a predicted impact on Friday.

Ivan's powerful winds made it a category four storm on the five-level Saffir-Simpson scale.

Twelve people were confirmed killed on Grenada and the toll is expected to climb, the Caribbean Disaster Emergency Response Agency (CDERA) said. A Trinidad radio station FM 95.5 said there were 24 dead in Grenada, but that was not immediately confirmed.

In the Dominican Republic, four youths drowned in rough surf churned by Ivan, civil defense officials said. There were also four dead in Venezuela, according to the national authorities, and one in Tobago.

At 0001 GMT the center of the storm was about 325 miles (520 kilometers) southeast of Kingston, the capital of densely populated Jamaica, the US National Hurricane Center said.

Jamaica and the Cayman Islands both issued hurricane alerts for their populations.

In a radio address to his nation, Prime Minister P.J. Patterson urged everyone to "remain calm and act responsibly as we face this imminent danger."

Storm surge flooding of 0.9 to 1.5 meters (three to five feet) above normal tide levels, along with large and dangerous waves, could be expected near the center of Ivan, the US hurricane center warned.

Rainfall of 12-18 centimeters (five to seven inches), possibly causing flash floods and mudslides, can also be expected, it added.

The deadly storm, which devastated Grenada, was moving west-northwest at about 24 kph (15 mph) a track that was expected to continue for the next 24 hours, the center said.

Authorities in Florida ordered tourists and mobile home residents to leave the Florida Keys, an island chain at the tip of the southeastern US state.

Cubans also made preparations in case the hurricane hits the island, nearly one month after Hurricane Charley left five people dead there and an estimated one billion dollars in damage.

Grenada, a tiny island nation of 90,000 inhabitants, was 85 percent destroyed by the storm, according to Prime Minister Keith Mitchell. Power lines were down and hundreds of people have taken refuge in shelters.

Mitchell's official residence was destroyed and the prime minister took shelter on a British navy frigate, HMS Richmond.

"We have really taken a tremendous hit in every respect," Mitchell told BBC radio by telephone.

"You are talking hundreds of millions of dollars of damage," he said. "I have declared the country a national disaster and I have contacted our international friends and indicated that."

He said the main prison had been destroyed and all the inmates had escaped.

British sailors from HMS Richmond and the supply vessel HMS Wave Ruler, were helping the emergency operation in Grenada, Britain's Defence Ministry said. The two ships were on patrol in the Caribbean.

Grenada is a former British colony and remains a member of the Commonwealth with Britain's Queen Elizabeth II as its head of state.

The Commonwealth issued an international appeal for help for member nations in the affected area.

"I have been closely monitoring the various destruction Hurricane Ivan has caused in countries including Barbados, Saint Vincent and the Grenadines, Trinadad and Tobago, and especially Grenada," Commonwealth Secretary General Don McKinnon said.

"Natural disasters of this magnitude and the devastation they cause in our small member states in particular have always been a major concern of the Commonwealth family," he said, as he appealed to Commonwealth nations and international organisations for help.

"This is the biggest single-island disaster" that the CDERA has responded to, "because almost all of the island is wrecked," CDERA spokesman Terry Ally told AFP from Bridgetown.

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