Hurricane Georges bore down on the Florida Keys Thursday, and more than three-quarters of a million people as far north as Fort Lauderdale were advised to evacuate mobile homes and low-lying areas.

Forecasters predicted that Georges - already blamed for more than 110 deaths across the Caribbean - would slice through the Keys late Thursday or early Friday.Hurricane warnings were posted for four counties - Monroe, Dade, Broward and Collier - with a population of 3.8 million. The warnings meant that hurricane-force winds of at least 74 mph could arrive by 5 a.m. Friday. Georges could be the first major hurricane felt in southern Florida since Andrew, which caused $25 billion damage in Florida alone in 1992.

Forecasters said similar conditions were possible in five more counties farther north by Friday evening: Palm Beach and Martin on the Atlantic Coast and Lee, Charlotte and Sarasota counties on the Gulf Coast.

Advisories recommending residents of low-lying areas and mobile homes to evacuate were issued today in Dade, Broward, Collier and Sarasota counties. The evacuation advisories cover about 685,000 people; a mandatory evacuation order issued earlier in the Keys affects an additional 80,000.

In Cape Canaveral, on Florda's Atlantic coast, NASA ordered the Discovery back to its giant hangar Thursday night. The space shuttle had been rolled to its launch pad Monday for next month's scheduled mission with John Glenn.

The wide area of the advisories was based on uncertainty in the forecast: The longer Georges' center stays over Cuba, the less time it has to build before hitting the United States. But a slight shift in track could give Georges more time over water to rebuild into a major hurricane.

Looking down the road, Georges is expected to have plenty of time over the warm, open Gulf of Mexico to build into a threat to the northern gulf late Sunday night or Monday morning.

For the Keys, the wind was already starting to pick up. John and Sylvia Phillips, who live on a boat docked off Key West, had an uncertain future after they loaded backpacks and stuck out their thumbs to hitchhike to the mainland.

"We had to wait until last night to pick up a paycheck," said Phillips, a bartender. They made up their minds to leave during the night when "that boat started rocking," Sylvia Phillips said.

The hurricane was inland over Cuba, about 385 miles southeast of Key West, and moving west-northwest at 12 mph. Top winds of 75 mph, extending 35 miles from the center, were expected to increase.

Georges hit some Caribbean islands with 20-foot waves and storm surges 5 to 10 feet above normal tides. Some of the Florida Keys are as little as 7 feet above sea level. The highest point in Key West is 14 feet above sea level.

"It doesn't take much to flood those islands. With a storm surge of 4 to 6 feet, it's still going to cover a great deal," said Michelle Huber, a National Hurricane Center meteorologist.

By Thursday, thousands had fled along U.S. 1, the two-lane road connecting the slender, 110-mile string of islands.

"It's like a ghost town," said Jim Malloch, Monroe County's project manager. "There's very few people out. At least half, maybe more, of the people left."

The last major hurricane to directly strike the Keys was Donna in 1960. A hurricane hit Key West in 1846 - unearthing caskets, washing some remains out to sea and tossing bodies into trees. Now the cemetery is built on higher ground in the center of town.

Wednesday, the smell of fresh wood was in the air from all the sawing and drilling as people boarded up windows to protect their homes.

Only a few dozen stragglers populated the tourist strip that is normally host to thousands. Those remaining ran red lights, double-parked and generally disobeyed traffic laws.