Residents who try to ride out Hurricane Gustav will be making the biggest mistake of their lives, New Orleans Mayor Ray Nagin warned on Saturday.

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Nagin ordered a mandatory evacuation of New Orleans, directing residents of a city still recovering from Hurricane Katrina to flee the approaching Hurricane Gustav.

"You need to be scared. You need to be concerned. You need to get your butts out of New Orleans. This is the storm of the century," Nagin said.

Mandatory evacuations have been ordered for Westbank starting at 8 a.m. Sunday, and mandatory evacuations of the Eastbank will begin at noon.

"Riding it out would be the biggest mistake you could make in your life," Nagin said.

Nagin warned that no emergency services will be available to residents who choose not to leave.

Hurricane Katrina, which struck New Orleans in 2005, came ashore as a Category 3 storm. Gustav is expected to hit as either a Category 4 or 5.

The footprint of Katrina was about 400 miles when it hit. Gustav currently has a footprint of 900 miles and continues to grow.

Hurricane Gustav was menacing Cuba Saturday night with winds of nearly 150 mph as it continues its threatening march toward the U.S. Gulf Coast.

The National Hurricane Center said Gustav is an extremely dangerous Category 4 storm. It could mushroom into the worst category, Category 5, as it heads into the Gulf.

As of 11 p.m. Eastern time, a hurricane watch was in effect for the northern Gulf Coast from east of High Island, Texas, eastward to the Alabama-Florida border, including New Orleans and Lake Pontchartrain. That's the area devastated by Hurricane Katrina three years ago. Massive evacuations are under way as a precaution against a repeat of that disaster.

Gustav's eye is about 90 miles west of Havana, Cuba. People are being told not to go outside, with winds increasing rapidly as the eyewall passes.

The hurricane should cross western Cuba Saturday night and emerge over the southern Gulf of Mexico early Sunday, making landfall on the northern Gulf Coast on Monday.

Lines For Evacuation Buses Grow In New Orleans

The increase in the storm's intensity Saturday came as people lined up for buses to take them out of New Orleans. Evacuations are under way in Louisiana. Traffic is also heavier on main highways out of the city as residents head north. (Video)

A line well over a mile long Saturday stretched in six loops through the parking lot at Union Passenger Terminal. Under a blazing sun, many people led children or pushed strollers with one hand and pulled luggage with the other. Volunteers handed out bottled water, and medics were nearby in case people become heatsick.

More than 700 buses were to carry an estimated 30,000 people to shelters. (Video)

Many residents said the evacuation is more orderly than the one for Hurricane Katrina.

Nagin also said the city will have twice the police protection on hand compared with during Hurricane Katrina.

Oil Workers Nearly Evacuated

Royal Dutch Shell, BP and other oil companies are wrapping up evacuations and shutting down production as Hurricane Gustav churns into the Gulf of Mexico.

The U.S. Minerals Management Service said that as of midday Saturday, slightly more than three-fourths of the Gulf's oil production and nearly 40 percent of its natural gas output had been shut down.

Analysts said prolonged supply disruptions could cause a sudden price uptick for gasoline and other petroleum products.

The U.S. Gulf Coast accounts for about a-quarter of all domestic oil production and 15 percent of natural gas output. It's also home to nearly half the nation's refining capacity.

Mississippi Makes Plans

President George W. Bush on Saturday declared an emergency exists in Mississippi and ordered federal aid to supplement state and local efforts for Hurricane Gustav, reported WAPT-TV in Jackson, Miss.

Gov. Haley Barbour had sought the designation to get emergency services in place in advance of the storm. During a Saturday afternoon new conference, Barbour said contra flow will begin at 4 a.m. Sunday and last at least through midnight, making many of the major highways one-way escape routes.

The governor said hours could be extended if traffic remains heavy.

Barbour said all lanes of Interstate 59 from the Louisiana state line to Polarville will be northbound. He said all lanes of Interstate 55 from the Louisiana state line to Bogue Chitto will be northbound.

Barbour said southbound traffic will be re-routed.

Barbour warned residents of south Mississippi that while the track for Gustav takes it west of Louisiana, past hurricanes have been shown that they can turn east at any time.

The National Hurricane Center on Saturday called Gustav an "extremely dangerous" storm.

Bush is getting regular updates on Gustav. Bush spoke to the governors of Gulf Coast states by phone Saturday to check on preparations and pledge full federal support.

The military is flying critical care patients out of harm's way. FEMA is ready with water, food, generators, blankets and cots.

Gustav already has killed 81 people in the Caribbean.

Texas Prepares

In Texas, buses for possible evacuations were brought to Houston -- 250 will stage at Tully Stadium, reported KPRC-TV.

"We're close to the coast," Harris County Emergency Management Coordinator Mark Sloan said. "We want to be able to respond to our residents as quickly as possible."

North Texas officials said they were preparing hundreds of shelters for people getting out of the storm's path, reported Dallas station NBC 5.

Hospital patients from areas threatened by the hurricane will be flown to Dallas-Fort Worth this weekend.

Interstate 35 could become a major evacuation route, KPRC reported, and throughout north Texas, people were getting ready to house thousands of evacuees who could begin arriving as early as this weekend.

Officials said 100 school buses were headed from Dallas toward the strike zone, ready to help with large-scale evacuations, and Federal Emergency Management workers were loading up water and other emergency supplies, from a logistics center in Fort Worth.

In Dallas, the Red Cross readied volunteers not only to head to the coast, but also to man shelters in north Texas. The organization will coordinate a statewide relief effort if needed.

Volunteers Head South

While millions of people get out of the Gulf Coast to get away from Hurricane Gustav, some Colorado Red Cross volunteers are going in, television station KMGH reported.

At Denver International Airport, Boulder resident and Red Cross volunteer David Turner was headed to Mississippi with his bags packed for up to three weeks of hard work.

"It?s a very rewarding experience," he said.

The American Red Cross Mile High Chapter, based in Denver, has already sent about 15 volunteers to the region and plans to send more, as part of the largest ramp-up operation since Hurricane Katrina.

"You just can?t afford not to be as prepared as possible. After what we saw happened after Katrina, how can we not prepare as much as we possibly can?" said Robert Thompson, with the Mile High Chapter. "Right now, we have supplies and personnel pre-positioned across the Gulf Coast, so no matter where Gustav hits, we?ll be ready to move in."

The Maryland National Guard is also headed south, television station WRC reported. Officials said they will prepare to support search and rescue missions, logistical air movement of supplies, air movement of evacuees and sandbagging of levee breaches.

Montgomery County, Md., urban search and rescue team, along with firefighters from Baltimore, Md., were also packing up to head for the Gulf Coast.

Arkansas Receives Early Evacuees

The first flight of New Orleans residents evacuating in advance of Hurricane Gustav arrived in Fort Smith Saturday afternoon.

The plane brought 65 people to the city, but as many as 4,000 people may stay there while the storm zeroes in on the Gulf Coast.

Officials at Fort Chaffee spent Saturday making sure everything was ready to house the evacuees. The site performed the same role during Hurricane Katrina in 2005, but leaders said they were more prepared and expected a smoother transition this time.

An agreement with the state of Louisiana limits the number of evacuees at Fort Smith to no more than 4,000. About half that number could arrive on buses either late Sunday or early Monday.

After arriving in Fort Smith, the evacuees boarded buses and rode to Fort Chaffee, where teams will take personal information from them to enter into a database for the Federal Emergency Management Agency.

"The process merely entails getting identification information on them," said Maj. Keith Moore of the Arkansas Army National Guard. "(That includes) their home address so FEMA can work with them in the aftermath, and the names of additional family members so that everyone is categorized on one sheet so we can keep people together and in touch."

Fort Smith?s Salvation Army is prepared to provide hot meals to the evacuees and a shuttle service will take them from Fort Chaffee into downtown so they can buy any personal items they might need.

Evacuees will also get medical screenings and anyone who needs medications will have access to them.