Flooding hit parts of New York’s Long Island and hundreds of thousands of people in New Jersey lost power Monday after a series of storms swept through the tri-state region.

The outages and flooding occurred after the city and much of the East Coast emerged from a heat wave.

Thousands of people lost power due to the storms. In New Jersey, they numbered more than 300,000, Gov. Phil Murphy said.

More than 123,000 customers in Monmouth County, south of New York City, and almost 60,000 customers in Ocean County were affected, according to Jersey Central Power & Light's website. The utility tweeted that "the damage is significant." In a statement Tuesday morning, PSE&G said crews restored power to 185,000 customers, and about 55,000 residents in New Jersey remain without power.

Murphy said the Board of Public Utilities was requesting mutual assistance in assessment and restoration efforts, which for some could take up to several days, as the state is faced with debris, downed trees and damage to the power grid.

"This storm packed a wallop. We were hit hard," the Ocean County Sheriff's Office said in a Facebook post Monday evening, urging people to not travel unless they have to because of downed wires.

The Monmouth County Sheriff's Office tweeted Monday night that 24 county roadways were closed due to downed wires and trees. In northern New Jersey, some residents reported heavy hail the size of nickels.

New York City didn't escape unscathed either. Video showed water cascading from the ceiling at a subway station in Brooklyn, and flooded roads were seen in Hempstead on Long Island and Mount Vernon, north of New York City.

The Gowanus section of Brooklyn flooded, NBC New York reported, and the water flooded at least one driver who abandoned his vehicle.

"I was scared because I was in sandals — you couldn’t see what was under you, but you could ... like, the water was at my waist, or almost at my waist," Amanda Denesha of Gowanus told the station.

Uber driver Walid Shaawon told NBC New York that the water was up to the rear passenger window of his sedan. He said he crawled out a window to escape.

Utility company Con Edison said that it had largely restored power to 33,000 customers in south Brooklyn who lost power Sunday due to equipment problems from the heat wave, but another 11,000 new outages throughout its service area were caused by Monday’s thunderstorms. Early Tuesday, 15,000 were without power.

Its outage map showed early Tuesday that almost 4,000 customers were without power in Queens and nearly 2,000 were without power in parts of Brooklyn, and power was not estimated to be restored until Tuesday afternoon or evening.

More than 2½ inches of rain was recorded in parts of Nassau County on Long Island and Bergen, Essex, Hudson and Passaic counties in New Jersey also saw more than 2 inches of rain by 9:30 p.m. Monday, the National Weather Service said in a statement, citing unofficial observations.

Flash flood watches and warnings covered a stretch from Atlantic City in New Jersey, including Morristown and Newark, and north of New York City early Tuesday, according to the weather service. Flash flood watches were in place for New York City, southern Connecticut and northeast New Jersey until 8 a.m. Tuesday. Flights were canceled at both Newark International Airport and LaGuardia Airport on Monday evening and early Tuesday, as weather conditions caused flight risks.

The weather service said as much as 1 to 3 inches of rain fell on the tri-state area Monday. While the flash flooding threat had diminished Monday night into Tuesday morning, localized flash flooding could still occur if any more heavy rains fall on already saturated areas, the weather service said.