A flood warning remained in effect until Tuesday morning for parts of New Jersey, while the slow-moving summer storm was expected to continue showering the Mid-Atlantic region into the middle of the week, according to the National Weather Service (NWS).

"A moisture-rich Summer-time airmass over much of the eastern/central US will continue to lead to areas of scattered to widespread thunderstorms capable of heavy downpours and flash flooding," the government forecaster wrote.

Torrential rain inundated parts of New York, New Jersey, Pennsylvania and Maryland on Monday night.

In New York City, emergency officials told people living in low-lying areas or ubiquitous basement apartments to head to higher ground.

Torrents of filthy rain water cascaded down Manhattan's major avenues around the time of the evening rush hour, and commuters sought cover under building canopies and bus stops.

Several major stations in the city's subway system were flooded, with passengers sharing images on social media showing waves of water gushing past ticket barriers and onto the electrified tracks.

In downtown Manhattan, dozens of passengers were reportedly trapped on a train as water poured into the 28th street station.

JFK, LaGuardia and Newark airports temporarily suspended departures Monday night, forcing the cancellation of dozens of flights.

FOX Forecast Center meteorologist Christopher Tate said the Big Apple overnight endured its "second wettest single hour ever recorded."

The city is no stranger to extreme weather.

Hurricane Sandy in 2012 killed more than 40 New Yorkers and destroyed approximately 300 homes.

Hurricane Ida in 2021 left more than a dozen dead in New York City, and damage to the subway took years to repair.

- State of emergency -

New Jersey Governor Phil Murphy declared a state of emergency, urging people to stay indoors.

Rescue workers in Scotch Plains, New Jersey waded into gushing floodwaters armed with red flotation devices after several drivers became stranded in the sudden surge, CBS footage showed.

Authorities across the region, including as far south as North Carolina, warned of hazardous driving conditions.

The NWS urged drivers encountering flooded roads to "turn around."

"Most flood deaths occur in vehicles," it said.

In Lancaster Pennsylvania, severe flash flooding prompted a disaster declaration, while emergency responders plucked people from flooded basements and conducted 16 water rescues.

"Intense rainfall dropped over 7 inches of rain in less than five hours," the fire department in the county's Mount Joy Borough posted on Facebook.

Staten Island recorded four to six inches (10 to 15 centimeters) of rain Monday night, according to the New York borough's emergency notification system.

Zohran Mamdani, the Democrat running for mayor of New York, wrote on social media that the rapid flooding emphasized the need for climate-proofing the city.

"We must upgrade our infrastructure for this new climate reality," he wrote.

The latest bad weather follows historic Fourth of July flooding that devastated parts of central Texas, killing at least 131 people, including three dozen children, and leaving more than 100 people still missing.

And in North Carolina, at least five people were killed when Tropical Storm Chantal slammed the coastal state last week, Governor Josh Stein said.

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