Hurricane Laura, currently bearing down on Texas and Louisiana, may bring a 20ft (6m) storm surge that would be “unsurvivable” and capable of sinking whole communities, forecasters have warned.
Laura is rapidly gaining momentum and shows no sign of weakening, raising concerns it could come ashore as a Category 4 hurricane – the second highest.
More than half a million people were ordered to leave their homes near the Texas-Louisiana state line.
In just 24 hours, the storm grew nearly 70% in power and reached a Category 3 status.
Golf carts are parked on higher ground in Sabine Pass, Texas, ahead of Hurricane Laura
It continued to draw energy from the warm Gulf of Mexico waters and was on track to arrive late on Wednesday or early on Thursday as the most powerful hurricane to strike the US so far this year.
“This is shaping up to be just a tremendous storm,” Louisiana governor John Bel Edwards told The Weather Channel.
A Category 4 hurricane can cause severe damage that may have lasting impacts for months in some places, and wide areas could be uninhabitable for weeks or months.
Hurricane warnings were issued from San Luis Pass, Texas, to Intracoastal City, Louisiana, and reached inland for 200 miles (322km).
Storm surge warnings were in effect from Freeport, Texas, to the mouth of the Mississippi River.
President Donald Trump urged coastal residents to flee their properties.
He tweeted on Wednesday: “Hurricane Laura is a very dangerous and rapidly intensifying hurricane.
“My Administration remains fully engaged with state & local emergency managers to continue preparing and assisting the great people Texas, Louisiana, and Arkansas.
“Listen to local officials. We are with you!”
A main street in the business area of Lake Charles, Louisiana, is empty as people seek shelter
National weather service meteorologist Donald Jones warned: “Your life will be in immediate and grave danger beginning this evening if you do not evacuate.”
The hurricane is expected to batter the coast with heavy rainfall as it moves inland, causing widespread flash flooding in states far from the coast.
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Winds are expected to increase to 145mph (233kph) before landfall, pushing water on to more than 450 miles (724km) of coast from Texas to Mississippi.
Flood watches have been issued for much of Arkansas, with forecasters predicting heavy rainfall to arrive by Friday in parts of Missouri, Tennessee and Kentucky.
Laura is so powerful that it is expected to become a tropical storm again once it reaches the Atlantic Ocean – potentially causing damage to the northeastern US.
Officials have advised people to stay with relatives or in hotels to avoid spreading the virus that causes COVID-19.