Hurricane Ida has claimed its first fatality with a person being crushed to death by a falling tree.
The storm system has caused a major power outage in the city of New Orleans with all 45m residents losing power.
Entergy New Orleans said because of "catastrophic damage to (their) transmission system, all of Orleans Parish is currently without power."
All eight transmission lines that deliver power into the city are out of service at this hour, according to Entergy.
The power cut has caused major issues with hospitals treating dozens of Covid patients, many of whom are on ventilators.
Ida has weakened into a Category 2 storm on the Saffir-Simpson scale, but will continue to produce damaging winds and flash floods in portions of southeastern Louisiana, the National Hurricane Center (NHC) said on Sunday.
President Joe Biden has agreed to a major disaster declaration for Louisiana which will free up federal funds.
“APSO reports first death related to Hurricane Ida. Shortly after 8.30pm deputies received reports of a citizen possibly injured from a fallen tree at a residence off of Highway 621 in Prairieville.
"Deputies arrived on scene and confirmed that the victim is now deceased,” The Ascension Parish Sheriff’s Office said in a post on their Facebook page.
State governor John Bel Edwards earlier warned: "This will be one of the strongest hurricanes to hit anywhere in Louisiana since at least the 1850s."
It is the toughest test yet for the hundreds of miles of new levees built around New Orleans after the devastation of Hurricane Katrina, which made landfall 16 years ago to the day, killing more than 1,800 people.
The state is also dealing with the nation's third-highest rate of new Covid-19 infections, with about 3,400 new cases reported on Friday alone.
Hospitals were treating some 2,450 Covid-19 patients, Edwards said, with those in many of the state's parishes already nearing capacity.
Ida slammed ashore around noon near Port Fourchon, Louisiana, a hub of the Gulf's offshore energy industry, blasting the coast with hurricane-force winds extending 50 miles (80 km) out from the eye of the storm.
Flash flooding was reported by the National Hurricane Center across southeastern Louisiana. Residents of the most vulnerable coastal areas were ordered to evacuate days in advance of Ida.
Those riding out the storm in their homes in New Orleans, less than 100 miles inland to the north, braced for the toughest test yet of major upgrades to a levee system.
