Storm Laura was upgraded to a destructive hurricane on Tuesday and is forecast to make landfall along the Texas or Louisiana coasts on Wednesday night, after earlier causing 24 deaths in the Caribbean.
Maximum sustained winds are near 75 mph (120 km/h) with higher gusts, the US National Hurricane Center reported, with the storm expected to strengthen over the next day.
"Laura is forecast to reach the northwestern Gulf Coast at or near major hurricane intensity Wednesday night," the NHC said.
"There is the danger of life-threatening storm surge accompanied by large and dangerous waves" in places, and up to 12 inches (30 centimeters) of rain could cause flash flooding, it continued.
Texas governor Greg Abbott warned that the storm could reach Category 4 status, the second-highest, with winds of up to 156 mph.
"We need to be prepared," he said, especially as the state continues to struggle with the coronavirus pandemic.
In particular, he warned of the high winds that are expected to blow through the state's most forested area and the potential for tornadoes.
Compared to Category 3 Hurricane Harvey, which caused catastrophic flooding and killed 68 people in 2017, "this is going to be more of a wind event," the governor said.
Laura also threatens the major oil refining centers of Lake Charles, Louisiana and Beaumont/Port Arthur, Texas, located near the coast.
Evacuations have been underway since the morning in the areas most at risk, especially on the coast where the water could rise up to three meters.
Several emergency shelters opened on Tuesday in Texas, with health precautions to fight against the spread of the virus.
"COVID-19 is going to be in Texas throughout the course of the hurricane," Abbott said, calling on families who can afford it to take refuge in hotels or motels so they "can be isolated from others."
In New Orleans, Mayor LaToya Cantrell also called for health measures to be respected despite the threat of wind, rain and flooding.
"Don't forget COVID-19 with weather effects from Hurricane #Laura on the way," she said on Twitter.
The city's historic French Quarter was emptied of its tourists, while sandbags were piled up in front of the doorways of colonial-style buildings and the windows boarded up with plywood.
- 'It's crazy' -
New Orleans remains traumatized by Hurricane Katrina, which made landfall as a Category 3 storm in 2005, flooding 80 percent of the city and killing more than 1,800 people.
Sonya McCuller, who lived through that hurricane 15 years ago, says anyone who survived Katrina knows they cannot know what to expect.
"One minute you may think that it's not going to come, the next minute you're trying to prepare to make sure you don't get caught in it. It's crazy, but we're just going to see what the next one is going to do," she said.
Laura, which was 525 miles from Louisiana on Tuesday, caused flooding in Haiti and the Dominican Republic, where at least 24 people died.
In Cuba, it caused material damage but no deaths.
In the Gulf of Mexico, more than a hundred oil platforms were evacuated as a precautionary measure, stopping about 80 percent of oil production.
The Atlantic storm season, which runs through November, could be one of the busiest ever this year, with the Hurricane Center predicting as many as 25 named storms. Laura is the 12th so far.
Tropical Storm Marco -- which also churned through the Gulf of Mexico -- was downgraded from a hurricane and dissipated on Tuesday off the coast of Louisiana before reaching land.
Marco's weakening winds spared the Gulf what would have been twin hurricanes, unprecedented since records began 150 years ago.