A limousine carrying several couples to a birthday party failed to stop at an intersection in upstate New York and struck a parked vehicle, killing 20 people in the deadliest transportation accident in the United States in nearly a decade, according to authorities and a family member.

Everyone in the limousine died along with two pedestrians in the incident on Saturday afternoon in the town of Schoharie, police confirmed.

Eyewitnesses described seeing the SUV-style limousine shoot across a junction and hit another car before ploughing into people in a shop car park.

The cause of the crash is unclear.

The victims have not yet been officially named but the New York Times reports that they include four sisters and at least two pairs of newlyweds. All those killed were adults, police say.

It is America’s deadliest transport crash since 2009, said the chairman of the National Transportation Safety Board (NTSB), Robert Sumwalt.

Early reports suggested the car had been taking the group to a wedding reception but later reports said they were travelling to a birthday party.

State police said on Sunday that the passengers in the limousine, described as a 2001 Ford Excursion, would not have been required to wear seatbelts.

The driver was also killed in the crash, they said.