Hurricane Ivan, the Caribbean's most powerful storm in a decade, slammed into Jamaica on Friday afternoon, knocking out power, washing out roads and sending uprooted trees flying. The worst of the Category 4 storm was forecast to arrive late Friday before moving on to Cuba and already battered Florida this weekend.

Prime Minister P.J. Patterson declared a "public emergency" as police and rescue workers geared up for Ivan's full impact and potential civil disorder. "I appeal to everyone to continue to exercise extreme care and caution," Patterson told Jamaicans in a televised address.

At 10 p.m., the eye of Hurricane Ivan was 35 miles south of Kingston and moving west-northwest at 10 mph with sustained winds of 155 mph, according to forecasters. There were no immediate reports of death or injury, but local radio began reporting sporadic looting and gunfire after nightfall. About 8:30 p.m., radio reported that three gunshot victims were being treated at Kingston Public Hospital.

Kingston Mayor Desmond McKenzie said on local radio that even before the worst of the storm struck, flooding in the capital constituted a "major catastrophe."

Jamaican government officials urged 500,000 people living in the most vulnerable coastal areas to evacuate. It was unclear how many had moved to higher ground, but as of early evening, local radio reported that about 3,000 people were in government shelters across the island.

Patterson held out hope that "by some miracle we may at the last minute be spared the worst," but he appealed for people to move to schools, churches and auditoriums, where they would be better protected.

On Friday afternoon, many Jamaicans were staying put, awaiting the storm with resignation. "We can't stop it come," said Evadne Hall, a coal seller in downtown Kingston, speaking in the familiar Jamaican lilt. Motioning toward the gray sea a block from her home, where she said she would ride out the storm, she said, "We can't do nothing about it. It just have to flourish."

As the first strong blasts of the hurricane arrived in midafternoon, national television stations were knocked off the air. Officials at the national electricity company said technicians had shut down the island's entire power grid because of the danger posed by the many trees that had fallen across power lines.

According to TV reports, Patterson's emergency order gave police broad powers of arrest and detention during and after the storm in an effort to keep thrill-seekers off the streets and prevent looting.

Flooding was reported from the provinces of Portland and St. Thomas at the eastern tip of the island to the tourist resort center of Montego Bay in the northwest. Emergency sirens could be heard here in the capital city late in the afternoon, as the storm moved in from the island nation of Grenada, where it killed at least 26 people and caused massive destruction.

Local radio and television were broadcasting public service announcements, including one telling all KFC chicken restaurant employees that they should stay home Friday but be sure to report for work Saturday.

About 3 p.m. Friday, television reported that a woman with a 6-month-old baby had called for help because they were stranded in their flooded home in a low-lying neighborhood. At 5 p.m., RJR radio reported that a pregnant woman in Kingston was giving birth; the roof of her house had been blown off, and she was unable to contact emergency medical officials.

"If there was ever a time to be a good neighbor, it's now," a newscaster said. "Be your brother's keeper."

At St. Joseph's Hospital, all non-emergency patients had been sent home, and about 31 elderly patients were being moved into a maternity ward where only a single mother and her new baby remained, said Elin Gabriel, a nurse and Roman Catholic nun. Gabriel said that hospital workers planned to tape and board up the maternity ward's windows Friday and that they had stocked up on extra water and food.

"We're just braving it out and cheering everybody on. We're all in this together," said Nadine Davis-Crosby, a nurse in the maternity ward, where the Weather Channel showed nearly nonstop footage of the enormous, swirling Ivan, which, in satellite images, was far bigger than the entire island of Jamaica.

More than 400 people sought shelter at the National Auditorium in the city center. Kerron Bailey, 26, and about 20 members of his extended family arrived at the shelter Friday morning from their home in Port Royal, one of the most vulnerable seaside communities in the area.

"It's better to be safe than sorry," Bailey said, as children played on the concrete floor and grandmothers sat silently on wooden bleachers, with blankets around their legs. "Some people needed a little persuading to come, but I talked them into it. We left just material stuff at home, and all that can be easily replaced with time."

Some of the people who declined to evacuate said that they had heard many storm reports over the years but that the last direct hit by a hurricane was Gilbert in 1988.

Fire officials in Port Royal, which sits at the end of a long peninsula that acts as a breakwater for Kingston Harbor, estimated that only half the town's 700 residents had left as of early Friday.

Port Royal is reached by a six-mile road down the narrow peninsula, which was pummeled by 20-foot waves late Friday. Kingston's airport is also along the road. At least 10 Air Jamaica and American Airlines jets sat on the tarmac Thursday afternoon, but there were no planes at the airport Friday.

Port Royal is at sea level, or perhaps even a little below in places. It is a small, quaint cluster of whitewashed buildings, most of which have tin roofs. Since the destruction of Gilbert in 1988, some new concrete houses have been built. But many of the structures are little more than shanties, and they are surrounded on three sides by water.

A large white Volvo bus was parked in the town's small center, a few feet from the waves, as residents piled aboard with bags full of supplies to go to the shelter at the National Auditorium. Angela McLean, 33, and her son, Christoff, 8, hurried aboard loaded down with food, pillows, clothes and important personal papers stuffed in garbage bags and a small backpack.

"I know this is God's work, but I'm scared and I'm leaving," she said. "I don't like the sea."

Roy Brown, 44, stood next to her and scoffed. He had sent his wife and child to the shelter, but he said he was staying behind.

"I'm not leaving," he said. "What's to be must be. I can't run from that."

The mixed feelings were evident across Port Royal, as some young men stood on the sidewalk casually smoking marijuana as a fire truck raced by, its siren wailing to try to spur people into leaving. While some people rolled suitcases and hauled bags to the evacuation bus, others enjoyed a leisurely morning drinking Red Stripe beer at Kevin's Sea Food, a small outdoor restaurant near the beach.

Tyrone Paisley, 29, and a friend stood on a street corner in a light rain and talked about how Port Royal had so little crime that "you can sleep on the sidewalk and people leave their windows open." Asked how that would help in a hurricane, Paisley shrugged: "We don't fear anything. Father God will turn it for us."

Down by the concrete Customs House, where open boats had been hauled out of the water and stacked on the beach and in the street, customs officer Peter Limton hustled toward his front door. He had a length of rope in his hand to tie down an awning that looked like it could blow away. He said many of the people in Port Royal think of the place as more than their home; because many of them are fishermen who earn their living from the sea, Port Royal seems more like their ship.

"We're going to ride it out," he said. "The captain goes down with the ship. The captain cannot leave the ship."

Ivan is seen as a strong Category 4 hurricane in this National Oceanic and Atmospheric Administration satellite image taken Friday afternoon. Nicolas Taylor, center, chops up a tree that fell due to winds preceding Hurricane Ivan on a highway near Kingston. A Jamaica Red Cross volunteer, Raquel Bremmer, speaks with residents at the National Auditorium where more than 400 people sought shelter.