Authorities told people along Louisiana's Gulf coast to take the coming threat of Hurricane Katrina very seriously.

"Ladies and gentlemen, this is not a test. This is the real deal," New Orleans Mayor C. Ray Nagin said at a news conference on Saturday.

He said he would likely be asking residents to evacuate their homes at daybreak on Sunday.

Michael Brown, head of the Federal Emergency Management Agency said those residents should leave within 36 hours because "beyond that, it's just too late."

However, up to 100,000 people lack the transportation to leave New Orleans, which sits below sea level, making it especially vulnerable to a powerful hurricane. Authorities may use the Superdome as a shelter of last resort.

Katrina is gaining strength over the warm waters of the Gulf of Mexico. The hurricane is expected to hit land Monday morning somewhere between New Orleans and Pensacola, Fla.

When the hurricane hit southern Florida on Thursday night, seven people died -- and it was only a Category 1 storm then. Experts predict it will be a Category 4 storm with winds of at least 210 km/h when it next hits land.

"Right now, it looks like Louisiana is in line for a possible direct hit," Louisiana Gov. Kathleen Blanco said. "It does not bode well for southeastern Louisiana."

Mandatory or voluntary evacuations were called on Grand Isle, Louisiana's only inhabited barrier island, and in the parishes of St. Charles, Lafourche, Terrebonne, Plaquemines and St. Bernard.

Coastal residents took the warnings seriously. They jammed highways and swamped gas stations as they scrambled to escape the coming hurricane. To aid the evacuation, Louisiana and Mississippi made all lanes on interstate highways into northbound lanes.

Some service stations were running low on gas by Saturday afternoon.

About 300,000 residents of low-lying areas of the Florida Panhandle east of Pensacola were also under voluntary evacuation orders.

Florida cleaning up

Katrina, the second hurricane to strike Florida this year, formed over the Bahamas on Wednesday.

When the hurricane made landfall along the Miami-Dade and Broward County lines Thursday night, sustained winds were measured about 129 km/h.

Residents of southeast Florida are still cleaning up. Utility crews are working to restore power to 733,000 homes and businesses, down from the more than 1.3 million customers left in the dark at the storm's peak.

Officials are supplying ice and bottled water at no charge.

Independent forecasting firms have pegged insured losses from Katrina's first landfall at between $600 million US and $2 billion US.

Katrina is the 11th named storm of the Atlantic hurricane season. That is seven more than typical by this time of year. The season began June 1 and ends Nov. 30.

With a report from CTV's Denelle Balfour