A major disaster has been declared in Louisiana as Hurricane Ida arrived with winds of 150mph.
More than one million homes are without power and New Orleans was blacked out in a massive power cut.
The sheriff's office in Ascension Parish, near Baton Rouge, reported a 60-year-old man had been killed when a tree felled by the powerful storm crashed on to his house.
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High winds tore part of the roof off a hospital in the town of Cut Off, Louisiana, just inland from the Gulf of Mexico. The hospital said it had suffered "significant damage" but that its patients were safe.
The White House said US President Joe Biden had declared the major disaster, which makes federal funds available to aid recovery efforts in the areas hit by the hurricane.
Hurricane Ida blasted ashore along the Louisiana coast on Sunday, with the eye of one of the most powerful storms ever to hit the US arriving near the barrier island of Grand Isle.
The powerful Category 4 storm made landfall on the same date Hurricane Katrina ravaged Louisiana and Mississippi 16 years earlier, about 40 miles west of where Category 3 Katrina first struck land.
Arriving with a barometric pressure of 930 millibars, Ida preliminarily goes down as tied for the fifth strongest hurricane to make landfall in the United States based on wind speed. Based on central pressure it is tied for ninth strongest US landfall.
Ida rapidly intensified overnight as it moved through some of the warmest ocean water in the world in the northern Gulf of Mexico, its top winds grew by 45mph to 150mph in five hours.
Hurricane force winds started to strike Grand Isle on Sunday morning.
Before power was lost on the Louisiana barrier island, a beachfront web camera showed the ocean steadily rising as growing waves churned and palm trees whipped.
Wind tore at awnings and water began spilling out of Lake Ponchartrain in New Orleans.
Officials there said Ida's swift intensification from a few thunderstorms to massive hurricane over three days left no time to organise a mandatory evacuation of its 390,000 residents.
Mayor LaToya Cantrell urged residents to leave voluntarily. Those who stayed were warned to prepare for long power outages amid sweltering heat.
More than two million people live around New Orleans, Baton Rouge and the wetlands to the south.
The view from space
New Orleans hospitals planned to ride out the storm with their beds nearly full, as similarly stressed hospitals elsewhere had little room for evacuated patients.
And shelters for those fleeing their homes carried an added risk of becoming flashpoints for new infections.
Comparisons to the August 29 2005, landfall of Katrina weighed heavily on residents bracing for Ida.
A Category 3 storm, Katrina was blamed for 1,800 deaths as it caused levee breaches and catastrophic flooding in New Orleans and demolished oceanfront homes in Mississippi.
Ida's hurricane force winds stretched less than 40 miles from the storm's eye, or less than half the size of Katrina.
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