Torrential rain flooded parts of Connecticut and New York's Long Island, washing out roads, trapping people in cars and a restaurant, and sweeping two people into a river.

Two women died in the storms, which also caused problems in New Jersey late Sunday and early Monday, authorities said.

As much as 25.4 centimetres of rain fell on some parts of western Connecticut, coming down so fast that it caught drivers unaware as roads quickly turned into rushing rivers.

The bodies of two women who disappeared during the storm were recovered Monday in Oxford, Conn., about 56 kilometres southwest of Hartford, officials said. Both were Oxford residents. Neither was immediately identified by authorities.

The storm system that hit Connecticut on Sunday and then moved on to Long Island was separate from Hurricane Ernesto, which on Monday was over the open Atlantic Ocean but still expected to cause powerful swells, dangerous surf and rip currents along the U.S. East Coast.

William Syrett, an associate professor of meteorology and atmospheric science at Penn State University, referred to the Connecticut-New York system as "training thunderstorms."

"It's like each thunderstorm is a car on a train track, and so they just keep going over the same place," he said.

Connecticut Gov. Ned Lamont said more than 100 people were evacuated by search-and-rescue teams Sunday evening. In the town of Southbury, a bystander filmed as Lucas Barber waded through chest-deep water to help a man whose car had become largely submerged in a flash flood.

"I pulled over, grabbed some rope that's in the back of my car for emergencies, and threw my phone and wallet on the seat and ran out there," Barber told the New York Times.

Barber pulled the trapped driver, Patrick Jennings, out of the floating car along with his golden retriever.

"He got me all the way out of the water, the dog comes swimming up and the rest is history," Jennings told the Times.

Another dramatic rescue took place at a restaurant in Oxford, where the Brookside Inn became surrounded by a rushing torrent of water. Eighteen people trapped inside the building were rescued by firefighters, who stretched a ladder across the floodwaters to reach them.

The water was "literally enveloping this whole restaurant," Jeremy Rodorigo, a firefighter from the neighbouring town of Beacon Falls, said Monday. "And we were worried about the structural integrity of the restaurant because there were literally cars floating by and large objects hitting the building."

'An environmental and economic disaster'

The firefighters also rescued a woman and a small dog from an apartment next to the restaurant, Rodorigo said.

Ed Romaine, the executive of Long Island's Suffolk County, said hundreds of homes were affected by flooding and that mudslides covered the roofs of cars in some areas.

"We are dealing with damage reports throughout this county," said Romaine, who joined other officials at a news conference near a pond in Stony Brook, N.Y., where a dam breached and destroyed a section of a major road and flooded homes.

Dan Panico, the supervisor for the town of Brookhaven, N.Y., called the flooding "an environmental and economic disaster."

"Millions of gallons of water, turtles, fish, everything is downstream, along with the personal belongings of many of the houses that were flooded," Panico said, adding that repairs to Harbor Road alone would cost $10 million US.

Dozens of flights were cancelled at Newark Liberty, LaGuardia and John F. Kennedy airports.

The storms dropped about five to 10 centimetres of rain on most of northern New Jersey, causing minor to moderate flooding on roads, including the Garden State Parkway and other major highways, that left some motorists stranded. No deaths, injuries or property damage were reported in New Jersey.

Amtrak halted service between Philadelphia and New York's Penn Station for several hours on Sunday evening because of flooding on the tracks in New Jersey. Service was restored by Monday morning, though several trains between Washington, D.C., and New York were cancelled because of unspecified "equipment unavailability."

Flooding also suspended service on a branch of the Metro-North Railroad in Connecticut. And delays of up to 30 minutes were reported Monday morning on some New Jersey Transit train lines due to weather-related signal issues.

Penn State University's Syrett cited "perfect conditions" for the storms, thanks to the amount of moisture in the air and a slow weather system.

The unusual part was the amount of rain that fell over several hours, Syrett said, not the thunderstorms.