US President Joe Biden says "historic investment" is needed to deal with the climate crisis, as the north-east reels from flash flooding and tornadoes that have killed at least 45 people.
The US is facing climate-related destruction across the country and tackling it is "a matter of life and death", the president said.
New York City and New Jersey saw unprecedented levels of rainfall.
Some residents became trapped in flooded basements and cars.
Six states suffered loss of life:
- New Jersey Governor Phil Murphy said at least 23 people had died in his state - most of them stuck in their vehicles as the waters rose
- At least 14 people lost their lives in New York City, including a two-year-old boy. Eleven of them drowned while trapped in their flooded basements, officials said
- Five people died in Pennsylvania, while a state trooper in Connecticut was swept away as he responded to a call
- Deaths were also reported in Maryland and Virginia
President Biden has declared an emergency in both New Jersey and New York, enabling both states to receive federal funding to support local disaster relief efforts.
The impact of climate change on the frequency of storms is still unclear, but we know that increased sea surface temperatures warm the air above and make more energy available to drive hurricanes, cyclones and typhoons. As a result, they are likely to be more intense with more extreme rainfall.
The world has already warmed by about 1.2C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.
'Niagara Falls level of water'
New York City Mayor Bill de Blasio criticised weather experts, saying their forecasts were being "made a mockery of in a matter of minutes". He said he had been warned to expect between three and six inches (7.5 and 15cm) of rain over the course of the day. However a record 3.15 inches fell in Central Park in just one hour.
"The suddenness, the brutality of storms now, it is different," he said, adding that the latest extreme weather was "the biggest wake-up call".
New York Governor Kathy Hochul said: "We did not know that between 8:50 and 9:50 p.m. last night, that the heavens would literally open up and bring Niagara Falls level of water to the streets of New York."
Residents have been assessing the damage to property.
One man in Flushing, New York, said his house was prone to flooding "but what I saw last night is unimaginable". "I have never seen water coming in all directions," Tedla Asfaw, 60, told the BBC. "There's huge damage here. It's a big hit for us."
In New Jersey, a tornado flattened the state's largest dairy farm, ripping roofs off buildings and toppling several large silos.
Many cows were trapped under fallen sheds and some died, the owners of Wellacrest Farm wrote on their Facebook page. "Along with the devastating loss of homes in our neighbourhoods - we, as a community, suffered a great loss with the destruction of our farm."
In New York, some 835 people had to be rescued from stranded subway trains, police said on Thursday, after social media pictures showed water gushing into underground stations and tunnels.
Other footage showed cars floating down flooded roads, with cries of "help" being heard from inside. Nearly 500 vehicles were abandoned in New York, the Associated Press says.
Passengers on trains, planes and buses have been describing finding themselves stuck for hours without moving as the flooding made travelling impossible.
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