A swath of the US east coast, including New York City, was under alert Friday due to approaching storm Henri, which is expected to become the first hurricane to hit the New England area in decades.

Forecasters warned of violent winds, the risk of flash floods and surging seas as the storm churned in the Atlantic, with landfall expected on Sunday.

"Strengthening is forecast during the next day or so, and Henri is expected to become a hurricane tonight (Friday) or Saturday," the US National Hurricane Center (NHC) said in its latest bulletin.

Officials in the New England region -- which includes Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont -- warned people to get ready.

"All residents are advised to begin storm preparations today, and to pay close attention to local weather," said the office of Massachusetts Governor Charlie Baker.

His state, which will close parks and beaches from Saturday to Monday, was bracing for the high winds to knock out electricity for up to 300,000 locals, the governors office said.

A sign outside the local Town Hall warns people to prepare for high winds and flooding ahead of Tropical storm Henri
A sign outside the local Town Hall warns people to prepare for high winds and flooding ahead of Tropical storm Henri AFP / JOSEPH PREZIOSO

NHC forecasters said Henri was packing sustained winds of nearly 70 miles (110 kilometers) per hour and threatened New York, as well as the neighboring New England states with potentially 10 inches (25 centimeters) of rain in some areas.

Storm "swells could cause life-threatening surf and rip current conditions," said the NHC bulletin.

If Henri strengthens as expected and stays on its current course, the storm would be the first hurricane to directly hit New England in 30 years.

"The last hurricane to make landfall onto New England was Hurricane Bob in 1991," Dennis Feltgen, an NHC spokesman, told AFP. That storm killed at least 17 people.

It's been almost a decade since such severe weather was expected in part of the region.

"The last time we had hurricane watches issued for the area was for Hurricane Irene, back in late August of 2011," tweeted the National Weather Service in New York City.