The unnamed local woman in her 60s was pulled from the car by a rescue swimmer dangling from a US Coast Guard helicopter about 50 yards from the American Falls, police said.

"We have never had a vehicle in the water this close to the brink," New York State Park Police Captain Chris Rola said in a press conference.

The woman was the only occupant of the car, which witnesses spotted floating down the river, Rola said.

Investigators believe the vehicle drove into the river in between a pedestrian and vehicle bridge but it's unclear what circumstances led to the incident.