Coastal residents jammed one-way interstates and gas stations Saturday as they rushed to get out of the way of Hurricane Katrina, which threatened to gain even more strength and make a direct hit on the New Orleans area.

"Ladies and gentlemen, this is not a test. This is the real deal," New Orleans Mayor 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 was a Category 3 storm with 115 mph sustained wind Saturday, but the National Hurricane Center said it was likely to gain force over the Gulf of Mexico, where the surface water temperature was as high as 90 degrees -- high-octane fuel for hurricanes. It could become a Category 4 storm with wind of at least 131 mph before reaching land Monday.

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

A hurricane watch extended from Louisiana to the Florida Panhandle, and large-scale evacuations were underway Saturday along the coast.

President Bush declared a state of emergency in Louisiana on Saturday because of the approach of Katrina, which could be especially devastating if it strikes New Orleans. The city sits below sea level, and is dependent on levees and pumps to keep the water out. A direct hit could submerging it in several feet of water.

In addition, 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 pickup 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.

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 11 p.m. EDT Saturday, the eye of the hurricane was about 335 miles southeast of the mouth of the Mississippi River and was moving west-northwest at nearly 7 mph, the hurricane center said. Offshore buoys indicated that 12-foot waves were approaching the coast.

"We know that we're going to take the brunt of it," said Louisiana Gov. Kathleen Babineaux Blanco (D). "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's famed Bourbon Street. "The problem is getting a taxi to the airport. There aren't any," said Brian Katz of New York.

Others tried to leave but could not get a flight. "We tried to move it up, but they told us they were all booked up," said Terry Evans of Cleveland, whose flight was supposed to leave Monday morning. "We may end up sleeping at the airport."

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

In Florida, utility crews were working Saturday to restore power to 733,000 customers, down from more than 1 million. Residents waited in lines that stretched for miles to reach centers distributing free water and ice.