NEW YORK -- The US states of New York and New Jersey on Thursday declared a state of emergency for areas under flash flood warnings, as heavy rain slammed the East Coast, threatened roads and disrupted air travel.

The National Weather Service said that heavy to excessive rainfall and potentially severe thunderstorms were expected along the Washington-Philadelphia-New York City corridor later Thursday afternoon and night. Some areas in the southern part of the region could see rainfall rates of 2 inches (5.08 cm) per hour.

"I am urging all New Yorkers to stay vigilant, stay informed, and use caution as we expect excessive rainfall with the potential for flash flooding," New York Governor Kathy Hochul said in a statement.

New York City Mayor Eric Adams and other local officials called on people to stay off the roads and urged residents in basement apartments to move to higher locations.

Air travel was disrupted due to heavy storms Thursday evening, with ground stops in effect at several major airports in New York, New Jersey, Philadelphia and Washington DC area, according to the Federal Aviation Administration.

Thousands of flights within, into and out of the United States were cancelled or delayed, according to FlightAware.com. New York's John F. Kennedy International Airport was experiencing average delays of around three hours.

Amtrak announced Thursday evening that trains between Philadelphia and Wilmington, Delaware, were stopped because severe storms sent high water over the tracks. "We are working to establish and provide a delay time. Once a route is available, anticipate residual delays," the company said on X.

One death has been reported in the storms. A child died after being trapped in water in Mount Airy, Maryland, said the local fire chief.

Flash flood and severe thunderstorm warnings were lifted in New York City by Thursday night, but people were still warned to avoid unnecessary travel.

Flood watches and severe thunderstorm watches posted in other locations remained in effect into Friday morning, with 4 to 6 inches (10.16 to 15.24 cm) of rain possible in some areas of the East Coast, according to the National Weather Service.