New York has declared a state of emergency after severe storms brought flash flooding. Many of the city's subway systems, streets and highways were flooded, while at least one terminal at LaGuardia Airport was closed Friday before reopening later.

Up to 20 cm of rain fell in some parts of the city, but the sky had cleared a bit by the evening.

"This is a dangerous, life-threatening storm," said Gov. Kathy Hochul. "I am declaring a state of emergency throughout New York City, Long Island and the Hudson Valley due to the extreme rainfall we are seeing across the region," Gov. Hochul wrote on X, formerly known as Twitter.

She urged people to take steps to stay safe and "never attempt to travel on flooded roads". No deaths or injuries have been reported.

A state of emergency was also declared in the New Jersey city of Hoboken, just across the Hudson River from New York City.

In New York City, Mayor Eric Adams warned people it was time for "heightened vigilance and extreme caution" after the state of emergency was declared.

"Some of our subways are flooded and it's extremely difficult to move around the city," he told a news conference. Despite the rain easing later on Friday, Governor Hochul warned "we are still struggling".

"My biggest concern right now is that people are going to see a decrease in rainfall and people are going to be out in their vehicles," she told CNN.

The flooding caused major disruptions to the New York City subway system and Metro North commuter rail service, according to the Metropolitan Transportation Agency. Some metro lines were completely suspended and many stations were closed.