New Jersey and  New York have declared a State of Emergency ahead of severe thunderstorms expected to unleash life-threatening flash flooding across the state. 

Meteorologists warned that up to seven inches of rain could fall through the evening, prompting flash flood watches until Friday morning. 

New Jersey Acting Governor Tahesha Way said: 'Beginning this afternoon, we are expecting severe thunderstorms to bring heavy rainfall and damaging wind gusts with the potential for flash flooding across the state.

'I urge all New Jerseyans to remain alert, follow all safety protocols, and monitor the proper channels for the duration of these storms. 

'Residents should remain off the roads and indoors unless absolutely necessary.' 

Governor Kathy Hochul announced a state of emergency for multiple New York counties around 3:00pm ET, telling residents to 'stay vigilant, stay informed, and use caution as we expect excessive rainfall with the potential for flash flooding.'

The state of emergency covers the Bronx, Delaware, Dutchess, Kings, Nassau, New York, Orange, Putnam, Queens, Richmond, Rockland, Suffolk, Sullivan, Ulster, Westchester, and contiguous counties. 

Flood watches are in effect for New York City, Long Island, and the Hudson Valley through Friday afternoon. 

The National Weather Service (NWS) warned there is up to a 70 percent chance of flash flooding in the East Coast states.

A slow-moving front and surge of moisture from the Gulf is bringing the heavy rainfall to the Northeast. 

AccuWeather warned that flooding is expected from New York City and Philadelphia to Baltimore and Washington, DC.

However, only New Jersey and New York have declared a State of Emergency.

New Jersey, home to more than nine million residents, is bracing for flash flooding, severe thunderstorms, intense rainfall and damaging wind gusts.

The NWS said rainfall totals of 1 to 3 inches are generally expected, with localized amounts of 5 to 7 inches possible. 

'These extreme weather conditions can result in landslides, rock slides, and flooded roadways,' said Way.

'Executive Order No. 394 declares a State of Emergency across all 21 counties, closing state offices early and allowing for resources to be deployed throughout the state during the duration of the storm.'

The NWS's New York office, covering Bergen, Essex, Hudson, Passaic and Union counties, warned of an 'elevated threat to life and property, particularly Thursday afternoon and Thursday night.'

Meanwhile, the Mount Holly office, which oversees the state's remaining 16 counties, said 'potentially significant flash flooding is possible this afternoon into tonight.'

New York is expected to see up to five inches of rainfall, with rates potentially exceeding two inches per hour.

'The Thursday evening commute will be impacted with areas of flash flooding possible and minor to moderate water level rises could occur on some waterways,' Hochul said.

'Some roads may become impassable from flooding, most likely around underpasses and roads with little or no drainage.'

AccuWeather meteorologists warned that the heavy rainfall may trigger delays and disruptions at major airports in the region, including Boston, New York City, Washington, DC and Baltimore. 

Major travel hubs, including LaGuardia Airport, Newark-Liberty International Airport, and Philadelphia International Airport have all announced ground stops until at least 5pm ET. 

Other major airports, including John F Kennedy International Airport, Boston Logan International Airport, and Ronald Reagan Washington National Airport, have announced ground delays lasting until at least early Friday morning.

The airport chaos has led to flight delays of more than three hours at New York's JFK Airport and New Jersey's Newark Airport.

Delays out of Washington's Ronald Reagan Airport, however, have now reached a staggering 268 minutes, or four and a half hours.

Flights at Philadelphia and LaGuardia have been delayed by more than two hours due to the dangerous storm.

According to AccuWeather, more 43 million people are in the path of potentially deadly flash flooding Thursday.