NEW YORK (AFP) - New Yorkers mopped up flooded homes and businesses and began removing fallen debris from crushed cars on Thursday (Sept 2) as they counted the cost of record rainfall that caught much of the Big Apple by surprise.

Under piercing blue skies that belied the carnage of just a few hours earlier, shocked residents surveyed the damage of a chaotic night that left at least nine people dead in the city and killed several more in outlying areas.

"I honestly feel heartbroken," said Marcio Rodrigues, at his destroyed car repair shop in the New York suburb of Mamaroneck, where several clients' cars were ruined.

"This was my dream. And I feel like I lost it all right now," he told AFP, crying.

A short distance away, electrical contractor Jim Lanza's ground-floor office was full of mud after water rose two metres high.

"It's pretty devastating," he said, adding that the water took about seven hours to recede.

Nearby, Jeannsie Silva Barrios recalled a sleepless night as the owner of her house pumped water from her basement.

"I was really scared. My husband had to wake up at like four o'clock in the morning just to see the water, how it was going," she said.

A few miles south, on Manhattan's Upper West Side, Jonas Sigle eyed the wreckage of his car outside his home.

"A 10-tonne tree just fell on my car. My car's crushed. It's totalled," he told AFP.

"Wow, this was just unbelievable," said his neighbour, Michael Price.

Record rainfall of 3.15 inches (over 8cm) fell in Central Park in just an hour, breaking a record set last month during Tropical Storm Henri.

Nearby, Metodija Mihajlov inspected the basement of his restaurant, which was flooded with 7cm of water late on Wednesday.

"When the rain started to get bad, my guys called me and we decided to close the restaurant and turn off the electricity and everybody left," he said.

"I've never seen that much rain ever," added the 50-year-old.

"It was like living in the jungle, like tropical rain."

"Luckily nothing was damaged. As soon as the rain stopped the water drained away," Mihajlov told AFP.

The flooding reignited memories of Hurricane Sandy, a more powerful storm that knocked out power for much of Manhattan and flooded subways in 2012.

Many residents posted videos on social media that showed water cascading down stairs and into apartments.

In Brooklyn, Rebecca Stronger was mopping up water from the basement and first floors of her veterinary clinic.

"We all show up, we all clean and we all get our job done," she told AFP.

'Hearts ache'

Stronger said she expects more storms in the future as the surface layer of oceans warms due to climate change.

"Of course. Everybody knows (about) climate change. The world is exploding on so many different levels. I expect it to happen a lot," she added.

The New York Police Department said nine people had died, eight of them trapped in basements and one in a car.

They were aged between two and 86 and were found mostly in flooded locations in Queens.

"Our hearts ache for the lives lost in last night's storm," tweeted Mayor de Blasio, who declared a state of emergency late Wednesday.

"Please keep them and their loved ones in your thoughts today. They were our fellow New Yorkers and to their families, your city will be there for you in the days ahead," he added.