ST. GEORGE'S, Grenada -- Hurricane Ivan took aim Thursday at Jamaica and possibly Florida after killing 23 people in five countries and devastating Grenada, where police fired tear gas to stop a looting frenzy.
Ivan, the deadliest hurricane to hit the Caribbean in a decade, pummeled Grenada, Barbados and other southern islands on Tuesday.
It weakened slightly and was downgraded Thursday from a Category 5 hurricane -- the most powerful -- to a Category 4 storm packing 150 mph winds but was still expected to pound Jamaica, where officials urged a half million people to evacuate coastal and flood-prone areas, today.
U.S. officials ordered people to evacuate the Florida Keys after forecasters said the storm -- the fourth major hurricane of a busy Atlantic season -- could hit the island chain by Sunday after crossing over Cuba. It was the third evacuation ordered there in a month, following Hurricane Charley and hard on the heels of Hurricane Frances.
Officials were also considering evacuating the 1,000 American citizens in Grenada, mostly university students who said they want to leave.
The storm left its worst damage in Grenada, where from the air it appeared that nearly every house had been ripped up.
In St. George's, Grenada's capital, police fired tear gas to try to stop a looting frenzy. Hundreds of people, including entire families with children, smashed hurricane shutters and shop windows to take televisions and shopping carts of food.
Troops from other Caribbean nations were on the way to help restore order.
In Jamaica, hundreds of tourists packed the airport of Montego Bay resort.
"Seeing other people panicked, I panicked as well," said Blanca Surino, 21, who was trying to persuade frazzled airport personnel to put her on a flight home to Los Angeles.
At the airport of Kingston, the capital, dozens of foreigners lined up for tickets.
Workers began bolting plywood boards to windows, and most businesses closed early.
Grocery stores and gas stations stayed open for long lines of people stocking up against the storm.
In the seaside town of Port Royal, just outside Kingston, fishermen pulled wooden skiffs ashore as menacing storm clouds rolled in. The town of squat concrete homes and zinc roofs was nearly wiped out by Hurricane Charley in 1951.
"It's Ivan the Terrible," said fisherman Peter Kission, 47. "We've been through this before. We can take another."
But 50-year-old Port Royal native Gabby Bess wasn't so sure. "If it hits us like Gilbert did, we'll be in a whole heap of trouble."
Hurricane Gilbert was only a Category 3 storm when it devastated Jamaica in 1988.
At 2 p.m. EDT, Hurricane Ivan was centered about 360 miles southeast of Kingston, Jamaica. Hurricane-force winds extended up to 60 miles and tropical storm-force winds another 160 miles. Ivan was moving west-northwest at 15 mph.
Ivan's outer bands hit Barbados' south coast on Tuesday, damaging some 220 homes. It also tore roofs from dozens of homes in St. Lucia and in Tobago, where a woman died. Its heavy rains flooded parts of Venezuela's coast and left four Venezuelans dead.
In Grenada, it killed 13 people and British sailors were treating about 100 injured at the hospital, where they restored generator power Thursday.
The British patrol boat HMS Richmond and a supply ship rushed to Grenada on Wednesday and provided communications for Prime Minister Keith Mitchell, whose home was damaged. Sailors said they had cleared the damaged and flooded airport runway for emergency flights.
Every major building in the capital, which boasts English Georgian and French provincial architecture, has suffered structural damage, U.N. spokesman Fred Eckhard said Wednesday.
Also devastated was the "spice isle's" agriculture, including its famous nutmeg crop, Mitchell said.
He also confirmed that the 17th century stone prison was "completely devastated," allowing convicts to escape, including politicians jailed for 20 years for killings in a 1983 left-wing palace coup that led the United States to invade. Nineteen Americans died in the fighting along with 45 Grenadians and 24 Cubans.
Ivan's outer bands brought drenching rain to Haiti's southwest peninsula overnight, where residents of sea-level Les Cayes town worried it would bring disaster equal to May floods that killed 1,700 people and left 1,600 missing and presumed dead along the Haiti-Dominican Republic border.
On the Net: