NEW YORK (AFP)

Heavy rain and strong winds battered the northeastern United States on Sunday as an unusually powerful autumn storm intensified, leaving tens of thousands without power and US media reporting one person dead.

New York, Boston and Philadelphia were all in the firing line of the "Nor'easter" -- so labelled for its northeasterly winds -- as authorities warned of potential major flooding and road closures.

The storm continued to dump rain during its "churn off the coast of the northern Mid-Atlantic and southern New England Saturday afternoon," the National Weather Service said in its latest forecast.

The storm was expected to move toward New Jersey and Long Island "through tonight, resulting in the full force of this Nor'easter" impacting the region by Sunday morning, forecasters said.

New York state Governor Kathy Hochul said the storm was bearing down Saturday on coastal areas of New York City and Long Island.

In Brooklyn, a 56-year-old man was killed when winds toppled a tree that struck him, US media reported.

Nearly 80,000 customers in New York, New Jersey, Connecticut, Massachusetts, Rhode Island and Pennsylvania were without power as of 1:30am (0530 GMT) Sunday, according to the monitoring tool poweroutage.com.

Up to 15 centimetres of rain are expected on Long Island over the next few days.

New York City Mayor Zohran Mamdani warned residents of the country's most populated city about strong wind gusts and the possibility of downed power lines, saying "Don't travel if you don't have to."

The storm forced the cancellation of hundreds of flights on Sunday, with 171 to and from Boston's Logan airport alone, and ongoing delays were reported across the region, according to tracker Flight Aware.

Major airlines including JetBlue, United, and American issued travel alerts allowing passengers to change their flights without incurring fees.

The United Nations, where world leaders are gathered for the organisation's General Assembly, urged media outlets covering the event to clear broadcasting equipment from outside the New York headquarters due to strong winds. Major cultural events were also called off.

British pop singer Ed Sheeran's weekend concerts near Boston were cancelled due to the storm, which had whipped up wind gusts of 113 kilometres per hour along the New England coast.

Nor'easters can occur throughout the year but are more frequent between fall and early spring. They are almost always accompanied by heavy rain or snowfall, as well as strong wind gusts.

Earlier this year, a Nor'easter that pummelled the northeast disrupted hundreds of flights and left thousands of homes and businesses without power. That storm came weeks after the region recovered from a devastating winter weather system that was linked to more than 100 deaths.