Hurricane Laura has made landfall in southwestern Louisiana as one of the most powerful storms to hit the state, with forecasters warning it could push a massive wall of water 65km inland from the sea.
Laura made landfall just before 1am on Thursday as a Category 4 storm packing winds of 240km/h in the small town of Cameron, Louisiana, the National Hurricane Center (NHC) said.
It rapidly weakened to a Category 2 storm on Thursday morning with maximum sustained winds of 168km/h as it moved north and battered southwest Louisiana, a marshy region particularly prone to storm surge and flooding.
Besides threatening life, the storm was barreling toward the heart of the US oil industry, forcing oil rigs and refineries to shut down production.
Laura's winds tore through Lake Charles, Louisiana all night, ripping roofs from buildings and shattering glass windows, videos posted to Twitter showed.
The city of 78,000 was seeing sustained winds of 137km/h and gusts up to 206km/h, in the hour after landfall, the NHC said.
"This is one of the strongest storms to impact that section of coastline," said David Roth, a forecaster with the National Weather Service.
"We worry about that storm surge going so far inland there because it's basically all marshland north to Interstate 10. There is little to stop the water."
Officials across the hard-hit area said it would be several hours before they could get out to begin search and rescue missions. Downed trees blocking roadways were expected to be the biggest immediate challenge for rescuers.
"Catastrophic storm surge, extreme winds and flash flooding continues in portions of Louisiana," the NHC said in an early Thursday bulletin.
About 620,000 people were under mandatory evacuation orders in Louisiana and Texas.
The storm surge could penetrate inland from Sea Rim State Park, Texas to Intracoastal City, Louisiana, and could raise water levels as high as six metres in parts of Cameron Parish, Louisiana, the NHC said.
"To think that there would be a wall of water over two stories high coming on shore is very difficult for most to conceive, but that is what is going to happen," said National Weather Service meteorologist Benjamin Schott at a news conference on Tuesday.
Most of Louisiana's Cameron Parish would be under water at some point, Schott added.
Laura could also spawn tornadoes on Thursday over Louisiana, Arkansas and western Mississippi and was expected to drop heavy rain over the region, the NHC said.