NEW YORK (NYTIMES) - In the aftermath of a ferocious storm that killed more than two dozen people in four states, national and local leaders acknowledged on Thursday (Sept 2) that extreme weather events posed an urgent and ongoing threat.

The storm killed at least 43 people in New York, New Jersey, Pennsylvania and Connecticut and left more than 150,000 homes without power. States of emergency remained in effect across the region by midday Thursday, as officials sought to get a handle on the damage.

Speaking from the White House, US President Joe Biden said the damage indicated that "extreme storms and the climate crisis are here", constituting what he called "one of the great challenges of our time".

At a news conference in Queens on Thursday morning, Governor Kathy Hochul of New York said that she had received a call from Biden, who she said "offered any assistance" as the state assessed the damage from Ida, a storm that she said represented a new normal.

"We need to foresee these in advance and be prepared," she said.

The deluge of rain on Wednesday - more than 15cm fell in just a few hours - turned streets and subway platforms into rivers. Emergency responders in boats rescued people from the rooftops of cars. Hundreds of people were evacuated from trains and subways. A tornado in southern New Jersey leveled a stretch of houses. Some rivers in New Jersey and Pennsylvania were still rising.

The rain broke records set just 11 days before by Tropical Storm Henri, underscoring warnings from climate scientists of a new normal on a warmed planet. Hotter air holds more water and allows storms to gather strength more quickly and grow ever larger.

Many of New York City's subway lines remained at least partly suspended as of midday on Thursday, as was commuter rail service across the region. Airports were open, but hundreds of flights had been cancelled.

In New York City, the dead ranged in age from a two-year-old boy to an 86-year-old woman, police said. Some drowned in basement apartments in Queens, where a system of makeshift and mostly illegally converted living spaces has sprung up.

On Thursday afternoon, Governor Philip D. Murphy of New Jersey announced that at least 23 people in the state had died. They included four people found dead in an apartment complex in Elizabeth and two people were killed in Hillsborough, New Jersey after they became trapped in their vehicles, a spokesperson for the town said. Another death occurred in Passaic, New Jersey, where the Passaic River breached its banks and fish flopped in the streets.

Governor Ned Lamont of Connecticut announced that the state would lower flags to half-staff to honor Brian Mohl, a state police sergeant whose car was swept away by the floodwaters.

The 8cm of rain that fell in Central Park in one hour on Wednesday eclipsed the record-breaking one-hour rainfall of 5cm on Aug 21. The National Weather Service, struggling to depict the level of danger, declared a flash flood emergency in New York City for the first time.

In Bergen County, New Jersey's most populous county, County Executive James Tedesco, a former firefighter, said on Thursday, "We have not complete devastation but close to it. This is as bad as I've ever seen it."

The remnants of Ida swept across parts of southern New England on Thursday, flooding streets and homes but not causing the catastrophic damage that just hours earlier had paralysed the New York City area.

As of 11am on Thursday, more than 22cm of rain had fallen in New Bedford, Massachusetts, and nearly 18cm had fallen in Middletown, Connecticut.

Portsmouth, Rhode Island, was drenched with more than 20cm of rain, while about 10cm had fallen in Hudson, Maine, according to the weather service.

A tornado touched down around 1.45am in Dennis, Massachusetts, on Cape Cod, with winds of about 120km per hour, the weather service said.

The tornado caused minor damage to one house and some tree damage, but nobody was injured, according to Lt. Peter Benson of the Dennis Police Department.

"From talking to the people in the home, they realszed what was going on and they sheltered in the basement," he said.

The Massachusetts Emergency Management Agency said it had been in contact with communities across the state to determine the extent of the damage.

"At this time, the observed damage is mostly street flooding and other minor flooding as well as trees/power lines down resulting in scattered power outages," the agency said in a statement.

A road in Portsmouth had crumbled, and water service in the area was "extremely limited", the police there said.

In Waltham, Massachusetts, police shared an image of several school buses submerged in floodwater while the police in Bristol, Rhode Island, shared a photo of submerged cars and urged residents not to "attempt to drive around barricades or officers on posts" because they might not make it through the flooded streets.

In Northbridge, Massachusetts, roughly 70km southwest of Boston, police reported that the Blackstone River had flooded backyards and had reached roads.

At 11am, Amtrak announced that all service between Washington and Boston had been cancelled for the day.

The weather service warned of life-threatening flash flooding in urban areas, including on highways and below underpasses, and in areas near streams and small rivers.