Almost 800 rescued in St. John the Baptist Parish after Hurricane Ida

In a briefing with governors and mayors affected by Hurricane Ida, President Joe Biden vowed full government support.

"We're there to help you get back on your feet," Biden said.

Louisiana Gov. John Bel Edwards said he estimated nearly 2 million are without power.

Biden said, "We're in close contact with local electric providers to see what they need. They are all private providers. We don't control that, but we're doing all we can to minimize the amount of time it is going to take to get power back up."

In the meeting, Edwards touted the success of the levee system, saying none of them were breached. But, he added, "Damage is still catastrophic."

Edwards said a U.S. Coast Guard helicopter crew rescued seven patients from a hospital in Lafourche Parish after its roof was ripped off by the powerful winds.

-ABC News' Sarah Kolinovsky

At least one death has been reported in New Orleans, Mayor LaToya Cantrell said. Details have not been released.

This brings Ida's death toll to at least two. A 60-year-old man in Ascension Parish died Sunday when a tree fell on a home, officials said.

At an emotional news conference Monday, Cantrell said the "worse-case scenario" with Ida "did not happen."

"We did not have another Katrina … we should all be grateful," she said.

Cantrell said New Orleans has a few collapsed buildings but not widespread destruction.

However, power is out throughout the city, 911 is not available and there are small pockets of standing water from blocked drains. The mayor stressed that residents should shelter in place.

-ABC News' Alexandra Faul

Ida, one of the strongest hurricanes to make landfall in Louisiana, has dropped 18 inches of rain on parts of the state.

New Orleans has been hit with 13.7 inches of rain.

Numerous flash flood warnings remain in effect across parts of Louisiana, Mississippi, Alabama and the Florida Panhandle.

Ida is expected to weaken to a tropical depression Monday before bringing heavy rain and possible flooding to the Tennessee Valley Monday night through Tuesday.

By Wednesday and Thursday the storm will hit the Mid-Atlantic and the Northeast. The forecast calls for 4 to 6 inches of rain and possible flash flooding.

-ABC News' Melissa Griffin

Ida significantly damaged Louisiana's Ochsner Health system, though neither patients nor employees have been injured, hospital officials said Monday. 

About 65 patients at two of Ochsner Health's facilities have been evacuated, they said. Ochsner Health officials said they've also been asked to help evacuate about 100 patients from Terrebonne General Health System in Houma, Louisiana.

Terrebonne General Health System said it "suffered structural damages" and has no water from the parish. Terrebonne General said it's working to complete a "smooth transition of care" to other facilities."

-ABC News' Alexandra Faul