New Orleans was without power Sunday night as Hurricane Ida battered southeastern Louisiana on the 16th anniversary of Hurricane Katrina. 

The city said the Entergy utility suffered "catastrophic" damage to a transmission line.

Ida slammed the coastline Sunday as a Category 4 storm, then weakened to a Category 3 with 125 mph winds. The storm is unleashing damaging wind gusts over 80 mph in New Orleans, along with flooding rain.

As the storm charges inland, destructive winds and flooding rain could extend more than 100 miles through Baton Rouge.

Ida made landfall at 12:55 p.m. near Port Fourchon, La., with 150 mph winds and tied for the most intense hurricane on record to strike Louisiana.

Ida's surge has reached 4 to 7 feet in southeastern Louisiana and coastal Mississippi, engulfing roads, homes, businesses and marinas, and will test the New Orleans flood protection system, bolstered by a $14.5 billion investment after Katrina.

The roof was blown off a south Louisiana hospital with patients inside, in a visceral indication of how the storm has collided with an already strained health system.

President Joe Biden promised Sunday to "put the country's full weight" behind rescue-and-recovery efforts and noted that he signed emergency declarations for Louisiana and Mississippi in advance so that aid could be "surged."

Almost 1 million people in New Orleans and surrounding cities were put under a flash flood warning through Sunday night, while a "life-threatening" flash flood "emergency" was declared in some communities south of New Orleans, near the Mississippi River.

More than 700,000 customers have lost power in Louisiana, and authorities warn that widespread power outages could last weeks.

Amid wind gusts topping 80 mph and a citywide power outage, sheets of rain are drenching New Orleans and southeastern Louisiana, causing flooding.

The National Weather Service issued a flash flood emergency, the most dire flood alert, for the south shore area of metro New Orleans.

"This is a PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW!," the Weather Service wrote.

In a separate special bulletin, the Weather Service reported 4 to 8 inches has fallen in the region and an additional 4 to 8 inches expected.

"Observed rainfall rates over southeastern LA have generally been 1-2 in/hr through early evening, but rates over 2 in/hr have occasionally been observed as well," the Weather Service wrote.

Flash flood warnings cover not only the New Orleans area but also Houma to the southwest and Slidell to the east. Gulfport, Miss., is also under a warning.

In New Orleans, the warning is in effect until 1 a.m. Eastern time (midnight local time) for "life-threatening flash flooding of creek and streams, urban areas, highways, streets and underpasses."

Entergy New Orleans, the city's electricity supplier, said its facilities sustained "catastrophic transmission damage" from the tropical cyclone, the city tweeted.

"The only power in the city is coming from generators," New Orleans's Office of Homeland Security and Emergency Preparedness tweeted.

According to Entergy's tracker at about 9:15 p.m., 176,939 customers in Orleans Parish - where New Orleans is located - were without power. In Louisiana, an outage tracker's 8:59 p.m. update placed the statewide figure at 789,463 households without power.

The New Orleans Sewage and Water Board said it was using backup power systems, including turbines and generators, to supply electricity to its pumping stations, which are essential to control flooding in the city. Nearby Jefferson Parish was also under a water-boil advisory.

Some early photos and video from Port Fourchon, about 100 miles south of New Orleans, and Lafourche Parish, within which it resides, show extensive damage. Many homes had roofs peeled off, walls were blasted through in some cases, and a marina was swamped.

Video showed the roof of the Lady of the Sea General Hospital ripped off in Galliano, also in the parish.

Alyson Neel, a spokeswoman for the Louisiana Health Department, said officials are "aware" and "working closely" with the Lady of the Sea General Hospital, about 25 miles southeast of Houma.

"Once it is safe to do so, they will evacuate their small number of patients," she said. She said she could not immediately share more, calling it a "fluid situation."

It is not clear how many people were inside the hospital.

The Post could not reach the hospital Sunday evening, and the Louisiana Hospital Association did not immediately respond to an inquiry.

Residents of Lafourche Parish were ordered to evacuate. But fleeing Ida has been difficult for those in hospitals, with spiking coronavirus cases filling beds around the South.

Louisiana Gov. John Bel Edwards said earlier Sunday that "evacuating these large hospitals is not an option because there are not any other hospitals with the capacity to take them."

"We were able to evacuate over 20 nursing homes and rehab facilities and behavioral facilities and those sorts of things," he said on CBS's "Face the Nation." "But when you think in terms of hospitals, it is just not possible."

New Orleans officials said Sunday that they are confident their levee system will not fail as it did in Hurricane Katrina, allowing water to surge into the city. Their main worry: torrential rains.

The area is projected to get 15 to 20 inches of rain from Saturday into Sunday, authorities said at a midday news conference held just before Hurricane Ida made landfall. The downpour could exceed 3 inches per hour, overwhelming the city's drainage systems and causing flooding.

Leaders warned that the hurricane would cut people off from some city services. The police department is working at "100 percent," Police Superintendent Shaun Ferguson said, but at some point, it would "have to hunker down."

"Our health-care system, our hospitals are hunkering down," echoed Jennifer Avegno, head of the New Orleans Health Department. "They are caring for the patients that are within their walls. Our first responders will be unable to get to you. Please do not try to access a health-care or a hospital facility right now. We will be there for you when the storm passes, but the safest thing you can do is to stay put."