The northeastern United States was inundated Monday with heavy rain and flooding across several states a day after storms and flash floods washed out highways and killed one person in New York state.

Parts of New York, New Jersey, Connecticut, Pennsylvania, Massachusetts and Vermont were under flood warnings, with states in the region recording rapid rainfall and "life threatening" flash floods, according to the National Weather Service (NWS).

Heavy rains in New York state on Sunday turned streets into raging waterways, washing out bridges, leaving roads impassable and leading Governor Kathy Hochul to declare states of emergency in two counties.

The Orange County Emergency Management office on Monday confirmed that a 35-year-old woman had died in Highland Falls, in New York's Hudson Valley, where "historic floods" caused significant damage.

Hochul said the woman was swept to her death in a flash flood in the valley as she tried to evacuate her damaged house with her dog.

"Her fiance literally saw her swept away," the governor told reporters on Monday.

On Sunday Hochul said that up to eight inches (200 mm) of rain had created "life threatening conditions due to flash flooding."

On Sunday evening, more than 12,000 customers had lost electricity in the state, but by midday Monday that figure had dropped to 3,800, according to poweroutage.us.

Amtrak rail service was suspended between New York City and state capital Albany "due to severe weather conditions" as of 5:30 am, the company said in a statement.

Hochul said the rains appeared to be heading east to Vermont where law enforcement earlier reported severe rain in four counties, with several roads washed out and closed.

"The expected rainfall rate is 0.25 to 0.5 inches in 1 hour," NWS said in a state alert. "Flash flooding is already occurring" and "catastrophic flooding" was expected Monday in parts of the Vermont.

Governor Phil Scott declared a state of emergency.

"Swiftwater rescue teams have been staged in strategic locations throughout the state, should they be necessary to help with evacuations and rescues from floodwaters," Scott's office said in a statement Sunday.

The heavy rains washed out and closed highways, and stranded people in their cars and homes. Search and rescue teams were operating in several locations, according to various media reports.

NWS said it had received "multiple reports" of significant flooding and of persons trapped in vehicles in Orange County.

"Several additional inches of rainfall is expected through Tuesday morning as this system slowly moves eastward" and more flash flooding is possible, it said Monday.

Scientists say that climate change intensifies the risk of heavy rain because a warmer atmosphere holds more water.