MAPLEWOOD, NEW JERSEY (AFP, REUTERS) - Flooding killed at least 41 people, swept away cars, submerged subway lines and temporarily grounded flights in New York and New Jersey as the remnants of Hurricane Ida brought torrential rains to the region.

"I'm saddened to report that as of right now, at least 23 New Jerseyans have lost their lives to this storm," New Jersey Governor Phil Murphy told reporters, adding to earlier total death tolls of 18 and then 21.

New York City police said 12 people were killed, while another three died in the suburb of Westchester, officials said.

Three people also died near Philadelphia in Pennsylvania, an official there confirmed.

Emergency responders in rafts rescued people trapped in their homes and cars on Thursday. Some streets remained so badly flooded they resembled rivers.

Throughout much of the Northeast, residents woke to water-logged basements, power outages, damaged roofs and calls for help from friends and family members stranded by the sudden, ferocious rains.

Among the fatalities, three people were found dead in a basement in the New York City borough of Queens, while four residents of Elizabeth, New Jersey, perished at a public housing complex that city spokesman Kelly Martins said was "flooded out with eight feet (2.5m) of water."

Roadways turned treacherous in minutes as the storm tore through the region, trapping drivers in quickly rising floodwaters. In Somerset County, New Jersey, at least four motorists were killed, officials said.

"Sadly, more than a few folks have passed as a result of this," New Jersey's Murphy said at a briefing in Mullica Hill in the southern part of the state, where a tornado ripped apart several homes.

The hit to the Middle Atlantic region came three days after Ida, one of the most powerful hurricanes ever to strike the US Gulf Coast, devastated southern Louisiana, destroying entire communities.

In Conshohocken, a suburb of Philadelphia, the Schuykill River inundated hotels, warehouses and condominiums that line the river. Emergency squads on Thursday were waiting for the waters to recede before starting evacuations of possibly hundreds of people who live in nearby apartments, according to officials.

Record-breaking rain

Ida's remnants brought 15cm to 20cm of rain to a swath of the Northeast from Philadelphia to Connecticut and set an hourly rainfall record of 3.15 inches (nearly 9cm) for Manhattan, breaking one set less than two weeks ago, the National Weather Service said.

The 7.13 inches (18cm) of rain that fell in New York City on Wednesday was the city's fifth-highest daily amount, it said.

New York officials blamed much of flooding on the high volume of rainfall in a short space of time, rather than the daily total, which was within predictions.

"Because of climate change, unfortunately, this is something we're going to have to deal with great regularity," said Kathy Hochul, New York's newly minted governor.

The number of disasters, such as floods and heat waves, driven by climate change has increased fivefold over the past 50 years, according to a report released earlier this week by the World Meteorological Organisation, a UN agency.

US President Joe Biden said on Thursday said the federal government stood ready to provide "all the assistance that's needed."

The governors of New York and New Jersey, who declared emergencies in their states on Wednesday, urged residents to stay home on Thursday as crews worked to clear roadways and restore service to New York City subways and commuter rail lines serving millions of residents.

"Right now my street looks more like a lake," said Lucinda Mercer, 64, as she peered out her apartment window in Hoboken, New Jersey, just across the Hudson River from New York.

Mercer, who works as a crisis line fund-raiser, said flood waters were lapping halfway up the hub caps of parked cars.

Subway service in New York City remained "extremely limited" and was not likely to be restored until later in the day, the Metropolitan Transit Authority said.

Commuter rail to the city's northern suburbs, most New Jersey Transit rail services and Amtrak passenger service between Philadelphia and Boston were cancelled.

About 370 flights were canceled at New Jersey's Newark Liberty Airport.

'Humbled by Mother Nature'

Michael Wildes, mayor of Englewood, New Jersey, said the city's central business district was under water and some residents had to be evacuated to the library overnight.

"We are being humbled by mother nature in this last year and a half," Wildes told Reuters by phone.

Mark Haley of Summit, New Jersey, said getting back home after a 15-minute drive to a bowling alley to celebrate his daughter's sixth birthday on Wednesday night became a six-hour slog through flood waters that often left him trapped.

"When we got out, it was a war zone," said Haley, 50, a fitness trainer. When he made it home, he found almost two feet (0.6m) of water in his basement.

Nearly 170,000 electricity customers were without power on Thursday in four northeastern states that got the bulk of the rain overnight, mostly in Pennsylvania and New Jersey, according to PowerOutage.US, which gathers data from utility companies.