Hurricane Laura made landfall in southwestern Louisiana as a Category 4 storm on Thursday morning, the US National Hurricane Center (NHC) said.
The storm has since been downgraded to a Category 2 but is still extremely dangerous, with strong winds, torrential rains and rising seawater pummeling the Gulf Coast in the southern United States.
The storm, packing maximum sustained winds of 150 miles (240 kilometers) per hour, was located about 40 miles (70 km) east of Port Arthur, Texas, and expected to move inland across southwestern Louisiana. "Potentially catastrophic impacts will continue," the NHC tweeted.
Television images showed heavy rains hitting the coastal city of Lake Charles shortly after the eye of the storm made landfall around 1:00 a.m. local time (6:00 UTC).
Authorities had ordered over half a million people to evacuate their homes ahead of the hurricane, which is the most powerful storm to strike the US so far this year.
The area in the direct path of Laura is home to about 4 million people, but officials said most had left for safer areas under the evacuation orders. Sheriffs, police officers and other authorities said it would be several hours before they could safely begin search and rescue operations.
The National Guard said it had mobilized more than 1,000 members in Texas to help with the response, including 20 aircraft and more than 15 shelter teams.
The storm surge could penetrate up to 48 kilometers (30 miles) inland from the coastline between Sea Rim State Park, Texas, and Intracoastal City, Louisiana. The highest water levels are expected in 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. Most of Louisiana's Cameron Parish would be underwater at some point, he added.
"The word 'unsurvivable' is not one that we like to use, and it's one that I've never used before," said Schott of the storm surge.
Louisiana Governor John Bel Edwards said the state would close large stretches of a major highway, Interstate 10, in preparation for the storm. One highway in Louisiana was already covered in standing water as Laura's outer bands moved ashore.
In a radio interview on Wednesday night, Edwards talked of the "apocalyptic" language that meteorologists used for the storm. "The language I've heard from the National Weather Service I've never heard before... They're sending the stongest possible message about how serious this storm is," he said.
How dangerous is a Category 4 storm?
Winds in this category will cause "catastrophic damage," according to the NHC. The center states that winds will cause severe damage to well-built homes including to roofs and possibly exterior walls. The winds will also snap or uproot trees and blow down power poles. Power outages could last for weeks and most of the area will be uninhabitable for weeks or months.
The powerful storm has already devastated parts of the Caribbean, killing at least 24 people and damaging thousands of homes and electricity infrastructure.
Hurricane Laura is set to be even more powerful than Hurricane Katrina, which made landfall in Louisiana as a Category 3 storm in 2005, killing 1,800 people and costing $125 billion (€106 billion) in damages.
kmm, lc/stb (Reuters AP)