NEW ORLEANS — Rescuers set out in hundreds of boats and helicopters to reach people trapped by floodwaters and utility crews mobilized Monday after a furious Hurricane Ida swamped the Louisiana coast and made a shambles of the electrical grid in the sticky, late-summer heat.

One of the most powerful hurricanes ever to hit the U.S. mainland weakened into a tropical storm overnight as it pushed inland over Mississippi with torrential rain and shrieking winds, its danger far from over.

Ida was blamed for at least one death — someone hit by a falling tree outside Baton Rouge. But with many roads impassable and cellphone service knocked out in places, the full extent of its fury was still coming into focus.

Governor Expects More Fatalities and Weeks of Power Outage

Christina Stephens, a spokesperson for Gov. John Bel Edwards, said that given the level of destruction, “We’re going to have many more confirmed fatalities.”

The governor’s office said damage to the power grid appeared “catastrophic.” And officials warned it could be weeks before power is fully restored.

“For the most part, all of our levees performed extremely well — especially the federal levees — but at the end of the day, the storm surge, the rain, the wind all had devastating impacts,” Edwards said. “We have tremendous damage to homes and to businesses.”

All of New Orleans lost power right around sunset Sunday as the hurricane blew ashore on the 16th anniversary of Katrina, leading to an uneasy night of pouring rain and howling wind.

When daylight came, streets were littered with tree branches and some roads were blocked. While it was still early, there were no immediate reports of the catastrophic flooding city officials had feared.

Residents Deal With the Aftermath of Destruction

“I had a long miserable night,” said Chris Atkins, who was in his New Orleans home when he heard a “kaboom” and all the sheetrock in the living room fell into the house. A short time later, the whole side of the living room fell onto his neighbor’s driveway.

“Lucky the whole thing didn’t fall inward. It would have killed us,” he said.

The misery isn’t over for many. Stephanie Blaise returned to her home with her father in the Lower Ninth Ward of New Orleans after evacuating. It only lost some shingles. But without power and no idea when electricity would be restored, she didn’t plan to stay long.

“We don’t need to go through that. I’m going to have to convince him to leave. We got to go somewhere. Can’t stay in this heat,” she said.

Damaged Hospitals Create a ‘COVID Nightmare’

Four Louisiana hospitals were damaged and 39 medical facilities were operating on generator power, the Federal Emergency Management Agency said. Officials said they were evacuating scores of patients to other cities.

The governor’s office said over 2,200 evacuees were staying in 41 shelters as of Monday morning, a number expected to rise as people were rescued or escaped from flooded homes. Stephens said the state will work to move people to hotels as soon as possible so that they can keep their distance from one another.

“This is a COVID nightmare,” she said, adding: “We do anticipate that we could see some COVID spikes related to this.”

Interstate 10 between New Orleans and Baton Rouge — the main east-west route along the Gulf Coast — was closed because of flooding, with the water reported to be 4 feet deep at one spot, officials said.

Preliminary measurements showed Slidell, Louisiana, got at least 15.7 inches of rain, while New Orleans received nearly 14 inches, forecasters said. Other parts of Louisiana and Mississippi, Alabama and Florida got 5 to 11 inches.

National Guard, Local, and State Agencies Add to Rescue Efforts

Amid the maze of rivers and bayous around the New Orleans area, people retreated to their attics or rooftops and posted their addresses on social media with instructions for search-and-rescue teams on where to find them.

The Louisiana National Guard said it activated 4,900 Guard personnel and lined up 195 high-water vehicles, 73 rescue boats and 34 helicopters. Local and state agencies were adding hundreds of more.

Jefferson Parish in suburban New Orleans knew of 500 people who said they were going to stay in areas that were flooded, and it began sending out dozens of boats, Parish Council member Deano Bonano told WWL-TV.

State Working to Restore Power After Tower and Lines Destroyed

More than a million customers in Louisiana and Mississippi were without power, according to PowerOutage.US, which tracks outages nationwide. That left them without air conditioning and refrigeration in the dog days of summer, with highs forecast in the mid-80s on Monday, climbing to nearly 90 by Wednesday.

The hurricane twisted and collapsed a giant tower that carries key transmission lines over the Mississippi River to the New Orleans area, causing widespread outages, Entergy and local authorities said. The power company said more than 2,000 miles of transmission lines were out of service, along with 216 substations.

The storm also flattened utility poles and brought trees down onto power lines.

“We don’t know if the damage is something we can get up quickly,” Entergy New Orleans CEO Deanna Rodriguez told WWL-TV.

The governor said on Sunday that 30,000 utility workers were in the state to help restore electricity.

AT&T System Down, Making it Difficult to Check on Family

AT&T’s phone system was down all across southeastern Louisiana. Many people resorted to using walkie-talkies. The governor’s office staff had no working phones.

People who evacuated struggled to check on those who didn’t leave. Charchar Chaffold left from her home near LaPlace, Louisiana, for Alabama after a tree fell on her place on Sunday. She frantically tried to get in touch with five family members who stayed behind.

She last heard from them Sunday night. They were in the attic after water rushed into their home. Chaffold tried texting, but she didn’t know if their phones were dead and or service was out.

“They told me they they thought they was going to die, I told them they are not and called for help,” Chaffold said.

Ida’s Winds Fifth Strongest to Hit the Mainland

Farther south, emergency officials had not heard from Grand Isle since Sunday afternoon. About 40 people stayed on the barrier island, which took the brunt of the hurricane and was swamped by seawater, Jefferson Parish President Cynthia Lee Sheng told NBC.

Ida’s 150 mph winds tied it for the fifth-strongest hurricane ever to hit the mainland. Its winds were down to 45 mph early Monday.

In Mississippi’s southwestern corner, entire neighborhoods were surrounded by floodwaters, and many roads were impassable.

Ida was expected to pick up speed Monday night before dumping rain on the Tennessee and Ohio River valleys Tuesday, the Appalachian mountain region Wednesday and the nation’s capital on Thursday.

Forecasters said flash flooding and mudslides are possible along Ida’s path before it blows out to sea over New England on Friday.