NEW ORLEANS (AP) — Rescuers set out in hundreds of boats and helicopters to reach people trapped by floodwaters Monday, and utility repair crews rushed in after a furious Hurricane Ida swamped the Louisiana coast and ravaged the electrical grid in the stifling, late-summer heat.

Residents living amid the maze of rivers and bayous along the state’s Gulf Coast retreated desperately to their attics or roofs and posted their addresses on social media with instructions for search-and-rescue teams on where to find them.

More than 1 million customers in Louisiana and Mississippi — including all of New Orleans — were left without power as Ida, one of the most powerful hurricanes ever to hit the U.S. mainland, pushed through on Sunday and early Monday before weakening into a tropical storm.

The damage was so extensive that officials warned it could be weeks before the power grid was repaired.

As the storm continued to make its way inland with torrential rain and shrieking winds, it was blamed for at least two deaths — a motorist who drowned in New Orleans and a person 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. 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” — dispiriting news for those left without refrigeration or air conditioning during the dog days of summer, with highs forecast in the mid-80s to close to 90 by midweek.

In hard-hit LaPlace, squeezed between the Mississippi River and Lake Pontchartrain, rescuers saved people from flooded homes in a near-constant operation.

Debbie Greco, her husband and her son rode out the storm in LaPlace with Greco’s parents. Water reached the first-floor windows, then knocked down the back door and filled the brick home with 4 feet of water. They retreated to the second floor, but then screaming winds collapsed the roof.

They were finally rescued by boat after waiting in the only dry spot, five people sharing the landing on the stairs.

“When I rebuild this, I’m out of here. I’m done with Louisiana,” said Greco’s father, 85-year-old Fred Carmouche, a lifelong resident.

Elsewhere in LaPlace, people pulled pieces of chimneys, gutters and other parts of their homes to the curb and residents of a mobile home park waded through floodwaters.

The hurricane blew ashore on the 16th anniversary of Katrina, the 2005 storm that breached New Orleans’ levees, devastated the city and was blamed for 1,800 deaths.

This time, New Orleans appeared to escape the catastrophic flooding city officials had feared. And the governor said Louisiana’s levees, heavily overhauled since Katrina, “performed extremely well.” But he said the storm still inflicted “tremendous damage” to homes and businesses.

Stephanie Blaise returned to her home with her father in New Orleans’ Lower Ninth Ward after evacuating. It only lost some shingles. But with 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.

New Orleans police reported receiving numerous reports of theft and said they made several arrests.

The city urged people who evacuated to stay away for at least a couple of days because of the lack of power and fuel. “There’s not a lot of reasons to come back,” said Collin Arnold, chief of emergency preparedness.

Also, 18 water systems serving about 255,000 customers in Louisiana were knocked out of service, the state Health Department said.

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. The governor’s spokesperson said the state will work to move people to hotels as soon as possible to keep their distance from one another.

“This is a COVID nightmare,” Stephens 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 forecasters said New Orleans received nearly 14 inches. Other parts of Louisiana and Mississippi, Alabama and Florida got 5 to 11 inches.

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 more.

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 said.

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 tower had survived Katrina.

The storm also flattened utility poles, brought trees down onto power lines and caused transformers to explode with flashes that lit up the night sky.

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

AT&T said its wireless network in Louisiana was reduced to 60% of normal. Many people resorted to using walkie-talkies. The governor’s office staff had no working phones. The company sent a mobile tower to the state’s emergency preparedness office so that it could get some service.

Charchar Chaffold left her home near LaPlace for Alabama after a tree fell on it Sunday. She frantically tried to get in touch via text message with five family members who had stayed behind.

She last heard from them Sunday night. They were in the attic after water rushed into their home. “They told me they thought they was going to die. I told them they are not and called for help,” she said.

Ida’s 150 mph winds tied it for the fifth-strongest hurricane ever to hit the mainland. Its winds were down to 40 mph around midday 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.

This story is developing. Refresh for updates.

Reeves reported from LaPlace, Louisiana. Associated Press writers Janet McConnaughey in New Orleans; Emily Wagster Pettus in Jackson, Mississippi; Seth Borenstein in Kensington, Maryland; Michael Biesecker in Washington; Sudhin Thanawala in Atlanta; and Jeffrey Collins in Columbia, South Carolina, contributed to this report.