Hurricane Gustav roared into the oil-rich Gulf of Mexico on Sunday after destroying homes and roads in Cuba, and the mayor of New Orleans ordered residents to flee the "storm of the century" by morning.
The U.S. National Hurricane Center said Gustav weakened slightly but was expected to regain strength as it moves over warm waters toward the U.S. coast, becoming a Category 4 hurricane later Sunday.
Forecasters issued a hurricane warning for over 500 miles (800 kilometers) of U.S. Gulf coast from Cameron, Louisiana, near the Texas border to the Alabama-Florida state line, meaning hurricane conditions are expected there within 24 hours.
Even after slowing to Category 3 status before sunrise Sunday, Gustav packed top winds near 120 mph (195 kph).
Gustav was just short of top-scale Category 5 strength when it made landfall Saturday on mainland Cuba near the community of Los Palacios in Pinar del Rio _ a region that produces much of the tobacco used to make the nation's famed cigars.
At least 300,000 Cubans were evacuated from Gustav's path as screaming 140 mph (220 kph) winds toppled telephone poles and fruit trees, shattered windows and tore off the tin roofs of homes.
A Cuban reporter on the Isla de la Juventud south of the mainland reported that the hurricane had been like "the blast wave from a bomb."
"Buildings without windows, without doors," he said. "Few trees remain standing."
But there were no reports of deaths.
Cuban Civil defense chief Ana Isla said there were "many people injured" on the island of 87,000 people. Nearly all the island's roads were washed out and some regions were heavily flooded.
"It's been very difficult here," she said on state television.
Forecasters predicted that Gustav would increase to a Category 4 on Sunday with winds up to 155 mph (249 kph) before making landfall Monday along the U.S. Gulf coast.
More than 1 million Americans made wary by Hurricane Katrina took buses, trains, planes and cars as they streamed out of New Orleans and other coastal cities, where Katrina killed about 1,600 people in 2005.
Mayor Ray Nagin of New Orleans, which was devastated by Katrina, issued a mandatory evacuation order beginning 8 a.m. (1200 GMT) and warned that anyone found off their own property after it takes effect can be arrested.
Nagin called Gustav the "mother of all storms" and told residents to "get out of town. This is not the one to play with."
As dawn broke Sunday over the city under siege, bumper-to-bumper traffic was reported in nearly every direction as residents heeded orders to flee. Police and National Guard troops were on the streets, preparing to patrol evacuated neighborhoods.
City officials put an estimated 30,000 elderly, disabled and poor residents on buses and trains for evacuation.
Gustav already has killed 81 people by triggering floods and landslides in Haiti, the Dominican Republic and Jamaica.
Cuba's top meteorologist, Jose Rubiera, said the storm brought hurricane-force winds to much of the western part of Havana, where power was knocked out as winds blasted sheets of rain sideways though the streets and whipped angry waves against the famed seaside Malecon boulevard.
But Sunday morning no flooding could be seen in central Havana, and state radio said the damage was "minimal" in the capital of 2 million people, given the storm's size, although southeastern Havana remained without power and natural gas.
To the east, people began returning to their homes early Sunday, the radio said, and schools were to open as normal on Monday except in Pinar del Rio.
In the fishing town of Batabano, 31 miles (50 kilometers) south of Havana, evacuees returned to their pastel-colored homes to find many surrounded by knee-deep water.
"My house is full of water," said Aldo Tomas, 43, pulling palm branches from his living room. "But we expected more. We expected worse."
Tourist Lidia Morral of Barcelona, Spain, said Gustav forced officials to close beaches the couple wanted to visit earlier this week in Santiago, on the island's eastern tip. The storm also prevented them from catching a ferry from Havana to the Isla de la Juventud on Saturday.
"It's been following us all over Cuba, ruining our vacation," said Morral, who was in line at a travel agency, trying to make other plans. "They have closed everything _ hotels, restaurants, bars, museums. There's not much to do but wait."
At 8 a.m. EDT Sunday, the U.S. hurricane center said Gustav was centered about 375 miles (605 kilometers) southeast of the mouth of the Mississippi River and moving northwest near 16 mph (26 kph).
In the Gulf of Mexico, where about 35,000 people work staffing offshore rigs and production facilities, oil companies wrapped up evacuations in preparation for the storm.
More than three-fourths of the Gulf's oil production and nearly 40 percent of its natural gas output were shut down on Saturday, according to the U.S. Minerals Management Service, which oversees offshore activity.
The U.S. Gulf Coast accounts for about 25 percent of domestic oil production and 15 percent of natural gas output, as well as nearly half its refining capacity. Analysts say prolonged supply disruptions could cause a sudden price uptick for gasoline and other petroleum products.
Meanwhile, Tropical Storm Hanna was projected to move north of the Turks and Caicos Islands by late Sunday, then curl through the Bahamas by early next week before possibly threatening Cuba.
As it spun over open waters, Hanna strengthened slightly and had sustained winds near 60 mph (95 kph) early Sunday. The hurricane center warned that it could kick up dangerous rip currents along parts of the southeastern U.S. coast.
