"Ladies and gentlemen, this is not a test. This is the real deal," New Orleans Mayor C. Ray Nagin said at a news conference. "Board up your homes, make sure you have enough medicine, make sure the car has enough gas. Do all things you normally do for a hurricane but treat this one differently because it is pointed towards New Orleans."

Katrina gained strength overnight, become a Category 4 monster with 145 mph sustained winds as it moved over the warm waters of the Gulf of Mexico early Sunday.

The storm formed in the Bahamas and ripped across South Florida on Thursday, causing nine deaths, before moving into the Gulf of Mexico.

A hurricane watch extended from Louisiana to the Alabama-Florida border, and President Bush declared a state of emergency in Louisiana. His spokesman urged residents along the coast to heed authorities' advice to evacuate.

"At this juncture, all we can do is pray it doesn't come this way and tear us up," said Jeannette Ruboyianes, owner of the Day Dream Inn at Grand Isle, Louisiana's only inhabited barrier island.

Katrina could be especially devastating if it strikes New Orleans because the city sits below sea level and is dependent on levees and pumps to keep the water out. A direct hit could wind up submerging the city in several feet of water.

Making matters worse, at least 100,000 people in the city lack the transportation to get out of town. Nagin said the Superdome might be used as a shelter of last resort for people who have no cars, with city bus pick-up points around New Orleans.

"I know they're saying `Get out of town,' but I don't have any way to get out," said Hattie Johns, 74. "If you don't have no money, you can't go."

Owners of gas stations in and around New Orleans were forced to direct traffic as lines to the pumps stretched down surrounding streets. Gas stations were running low on gas by midafternoon Saturday

"I was in line at the bank for an hour and have been waiting for gas for 30 minutes," said John Sullivan. "If it's anything like they say its going to be, we don't want to be anywhere close to the city."

Louisiana and Mississippi made all lanes northbound on interstate highways. Mississippi declared a state of emergency and Alabama offered assistance to its neighbors. Some motels as far inland as Jackson, Miss., 150 miles north of New Orleans, were already booked up.

By 2 a.m. EDT Sunday, the eye of the hurricane was about 310 miles south-southeast of the mouth of the Mississippi River. It was moving west-northwest at about 8 mph and was expected to turn more to the northwest during the day, the National Hurricane Center said.

"We know that we're going to take the brunt of it," Louisiana Gov. Kathleen Blanco said. "It does not bode well for southeastern Louisiana."

Some tourists heeded the warnings and moved up their departures, and lines of tourists waited for cabs on New Orleans' famed Bourbon Street.

"The problem is getting a taxi to the airport. There aren't any," said Brian Katz, a salesman from New York.

But plenty of people in the French Quarter stayed put, and bars were rocking Saturday night.

"The only dangerous hurricanes so far are the ones we've been drinking," said Fred Wilson of San Francisco, as he sipped on the famous drink at Pat O'Brien's Bar. "We can't get out, so we might as well have fun."

New Orleans' worst hurricane disaster happened 40 years ago, when Hurricane Betsy blasted the Gulf Coast. Flood waters approached 20 feet in some areas, fishing villages were flattened, and the storm surge left almost half of New Orleans under water and 60,000 residents homeless. Seventy-four people died in Louisiana, Mississippi and Florida.

Katrina was a Category 1 storm with 80 mph wind when it hit South Florida on Thursday, and rainfall was estimated at up to 20 inches. Risk modeling companies have said early estimates of insured damage range from $600 million to $2 billion.

Nine people were killed in Florida as a result of Katrina, including two people discovered Saturday in their home after suffering apparent carbon monoxide poisoning from a generator.

South Florida utility crews were still working Saturday to restore power to about 700,000 customers, down from more than 1 million. Residents waited in lines that stretched for miles to reach state-operated centers distributing free water and ice for those without electricity.

Florida has been hit by six hurricanes since last August.

Katrina is the 11th named storm of the Atlantic hurricane season, which began June 1. That's seven more than typically have formed by now in the Atlantic, Caribbean and Gulf of Mexico, the hurricane center said. The season ends Nov. 30.