Storms prompted flash flood warnings across the New York City metropolitan area Monday night, with photos showing severe flooding across the city and in parts of New York state and New Jersey.

More than 50 million Americans throughout the Northeast are under flood watches on Monday, with a significant risk of flash flooding in some areas. Flash flood warnings have been issued for cities including New York City, Newark, New Jersey, and Arlington, Virginia -- including the Reagan National Airport -- through Monday evening.

The heavy downpours wreaked havoc across the city with footage showing commuters overwhelmed by floodwaters in various subway stations.

Following severe flash flooding on the East Coast, transport infrastructure in New York has been hit with travel disruption. New York City and New Jersey declared a state of emergency after heavy rainfall soaked the Northeast coast,

Heavy rains during the evening brought flooding, road closures and power outages throughout New Jersey, which is under a state of emergency.

Severe flash flooding across the tri-state area on Monday caused subway delays and road closures across the Big Apple and pushed New Jersey to declare a state of emergency. All five boroughs and Nassau County are under a flash flood warning through midnight.

The heaviest rainfall and the most widespread thunderstorms are expected to develop from Northern Virginia through southern New England in the afternoon. The Weather Prediction Center has issued a “moderate” (Level 3 out of 4) risk for flash flooding in that corridor through Tuesday morning.

The National Weather Service has expanded a warning for potential 'life threatening' flooding in NY to include Rockland and central .