Ivan's winds strengthened to near 155 mph - the most powerful Category 5 ranking - as the storm's center moved toward landfall at around 2 a.m. (1 a.m. MDT), the U.S. National Hurricane Center in Miami said.
But the hurricane was expected to spare the densely populated capital of 1 million people the brunt of its wrath.
Reports of sporadic gunfire and looting in Kingston reached the emergency management agency, said spokeswoman Nadine Newsome, but police could not confirm that.
Howling winds and sheets of horizontal rain crashed around the eastern end of the blacked-out island after utility officials turned off the power to minimize damage to plants.
Jamaican Prime Minister P.J. Patterson declared a public emergency and pleaded with the half million people considered in danger - about one in five islanders - to get to shelters. Many residents, however, refused to leave, fearing their homes would be robbed if abandoned.
''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.
Cuba declared a hurricane watch across the entire island Friday after its leader, Fidel Castro, went on national television warning residents to brace themselves.
In South Florida, long lines reappeared at gas stations and shoppers swarmed home building stores and supermarkets. Forecasters said Ivan could tear through the Keys as early as Monday, though there still was a chance it would instead move out into the Gulf of Mexico.
In Jamaica, awed onlookers stood transfixed on the seaside Palisadoes Highway near Kingston's airport as 23-foot waves crashed to shore, thrusting rocks and dead tree branches more than 100 feet into the road.
''I've lived here all my life and I've never seen anything like this,'' said businessman Chester Pinnock, huddled under an umbrella in the drenching rain.
Jamaicans can expect to feel the effects of the punishing hurricane through most of today, said Lt. Dave Roberts, a Navy meteorologist at the U.S. National Hurricane Center in Miami. It was projected to exit the island around Montego Bay, pass the Cayman Islands and cross over Cuba before taking aim at southern Florida.
Ivan became the fourth major hurricane of the Atlantic Season on Sunday. It damaged dozens of homes in Barbados, St. Lucia and St. Vincent Tuesday before making a direct hit on Grenada. It damaged 90 percent of homes there, tossed sailboats to shore and set off looting among some of the 100,000 residents left without electricity and water.
Grenada's Police Commissioner Fitzroy Bedeau said efforts to determine a death toll were hindered by blocked roads, landslides and lack of telephone service.
