KINGSTON, Sept 9: Jamaicans rushed to supermarkets and schools closed as Hurricane Ivan swept towards the Caribbean island with 160-mph (258-kph) winds on Thursday after killing at least 20 people on the tiny spice island of Grenada.

Jamaican Prime Minister P.J. Patterson urged Jamaica's 2.7 million people to get ready as Ivan grew to a monster Category 5 storm, the most intense on the hurricane scale.

"All persons should prepare to relocate to shelters as soon as the Office of Disaster Preparedness instructs them to," Patterson told Jamaicans. "It is better for us to breathe a sigh of relief, than for us to say, 'If we had known.'"

Hurricane-weary Floridians eyed the storm warily after the state was hit by two hurricanes, Charley and Frances, in the last month. Emergency managers in the Florida Keys ordered a mandatory evacuation for visitors, a measure taken well in advance because thousands of tourists need time to move recreational vehicles and boats up the 100-mile (160-km) island chain, linked by a single road.

An evacuation of Keys' residents was to begin on Friday. The Cayman Islands, a tiny British colony and key offshore financial center in the northwestern Caribbean, issued a hurricane watch for its 43,000 people on Thursday, telling them hurricane conditions were possible within 36 hours.

In Jamaica, some gas stations in the capital ran out of fuel and long lines formed at food stores. The government ordered schools closed on Thursday and Friday and three universities shut their doors.

'LOOKS LIKE A KILLER': Diplomatic missions shut down and the government urged employers to close by noon on Thursday. "This one looks like a killer. If it follows the same path, a lot of us will die," Kingston resident Jefferson James said. Ivan slammed into Grenada, a volcanic island of 90,000 people in the south eastern Caribbean on Tuesday, flattening or badly damaging homes and cutting power. -Reuters