Rescuers have set out in hundreds of boats and helicopters to reach people trapped by floodwaters, while utility repair crews have 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 one million customers in Louisiana and Mississippi – including all of New Orleans – were left without power as Ida, one of the most powerful hurricanes to hit the US mainland, pushed through on Sunday and early Monday (local time) 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 mobile phone service knocked out in places, the full extent of its fury was still coming into focus.

Christina Stephens, a spokesperson for Governor 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”.

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 1800 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.

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.

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 more than 2200 evacuees were staying in 41 shelters as of Monday morning. The number was 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 so that they can keep their distance from one another, describing the situation as a “COVID nightmare”.