-- People in the Florida Keys were ordered to flee and residents along hundreds of miles of Gulf Coast began boarding up Thursday as Hurricane Dennis took aim at the storm-weary region.

Forecasters warned residents from Florida to Louisiana that Dennis could be a major hurricane, with top winds already at 135 mph. The hurricane turned into a Category 4 storm Thursday evening as it gained strength while moving through the Caribbean toward the Gulf of Mexico. Five people were reported killed in Haiti, four when a bridge collapsed.

Many in the hurricane's projected path already got a wake-up call this week from a surprising Tropical Storm Cindy. It caused three deaths, knocked out power to thousands, and spawned twisters that toppled trees and caused as much as $40 million in damage to a famed NASCAR track.

"We're trying to get ready for whatever happens. We've been through so much already," Jose Davila said as he painted a house in Port Charlotte. Blue tarps still dot the rooftops of homes there, waiting to be repaired from Hurricane Charley, the first of a record four hurricanes to hit Florida last year.

"They're freaked out," Joe Hendrickson said of residents he encountered buying plywood and storm shutters at a Home Depot in nearby Punta Gorda. "They're taking it serious. They've seen what a hurricane can do."

Tourists across the Florida Keys were ordered to evacuate, as were all mobile home residents -- and all southernmost residents of the island chain. A hurricane warning was issued for the lower Keys.

Lines of cars were seen streaming out of the island chain Thursday. Airlines reported that nearly all flights out of Key West were full, and Greyhound added buses to help get residents out of the area.

At 11 p.m. Eastern time, Dennis's center was about 105 miles south of Camaguey in east-central Cuba, or roughly 500 miles southeast of Miami. It was moving northwest at about 15 mph on a path that could have the Keys and southwestern Florida feeling its effects Friday.

At Cape Canaveral, the space shuttle Discovery was considered to be safe on its launchpad for now, and NASA still aimed for a liftoff next week -- the first shuttle mission since the Columbia disaster.

But shuttle managers decided Thursday evening to begin initial preparations to move Discovery from the pad. A final call on whether to haul the shuttle back to its hangar was expected by Friday afternoon.

In Gulf Shores, Ala., residents still have not fully rebuilt the damage from Hurricane Ivan 10 months ago. Only about 60 percent of rental properties have reopened.

"I'm worried about flying trash cans and two-by-fours," said Nick Primozic.

In Louisiana, preparations for Dennis were delayed by the aftermath of Cindy, which caught many by surprise when it moved ashore Tuesday night. Cindy brought eight inches of rain and 70-mph winds that knocked out power to about 287,000 customers, the largest blackout since Hurricane Betsy 40 years ago.

An estimated 64,000 customers were still without power Thursday.

A highway sign in the Miami area announces the evacuation of the Florida Keys.