A state of emergency has been declared in New York City after intense rainfall turned expressways and subways into gushing rivers, and authorities warn the danger’s not over.

Areas like the Brooklyn neighbourhood were slammed by a month’s worth of rain in just a few hours on Friday (local time) during a chaotic rush-hour.

More than 76mm of rain had fallen on Friday, causing dangerous flash flooding, and another 76mm to 180mm was expected to follow.

The National Weather Service warned totals over 200mm “are increasingly likely”.

The city that never sleeps ground to a halt as what one reporter described as “sheets” of rain pelted down from every angle.

Tweet from @NYMag

Footage on social media shows water pouring into the underground subway and public transport passengers climbing onto their seats as flood levels rise.

Videos show busy streets drowning under metres of water that swamps businesses, submerges the city’s famous taxis and fills basements.

New York governor Kathy Hochul declared a state of emergency for New York City, Long Island and the Hudson Valley on Friday morning (local time).

“This is a very challenging weather event,” Hochul told New York’s WNBC-TV.

“This a life-threatening event. And I need all New Yorkers to heed that warning so we can keep them safe.”

Tweet from @observer888888

New York City Mayor Eric Edwards said the “dangerous weather condition” was “not over”.

“I don’t want those gaps in heavy rain to give the appearance that it is over, it is not.”

The weather service had earlier warned New Yorkers that “heavy to excessive rainfall and flooding” was possible.

The BBC reports that John F Kennedy International Airport has had its wettest day since record keeping began in 1948 with nearly 20cm of rain.

Tweet from @weatherchannel