Media playback is unsupported on your device Media caption The cause of the crash is unclear

Twenty people have been killed in a crash involving a stretch limousine taking people to a party in the US state of New York, police say.

All 18 people in the limousine died along with two pedestrians in the incident on Saturday afternoon in the town of Schoharie, police confirmed.

Witnesses 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.

What happened?

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.

Image copyright CBS Image caption Several police units were investigating the fatal incident

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

A reporter for local news site Spectrum News, Mercedes Williams, tweeted images and footage from the scene of the incident, which took place near a store and cafe on routes 30 and 30A in Schoharie County.

The images show a long line of emergency services vehicles lining the roads, which were closed to traffic.

Another image shared on Twitter showed a large vehicle that appeared to have veered off the road and crashed into a tree.

Eyewitnesses say a number of people entering and leaving the store were hit in Saturday's incident, local media report.

"I heard this loud bang, I saw a lot of people here at the Apple Barrel [store and cafe] out in the parking lot," said Bridey Finnagen, who lives nearby. "Then I heard screaming."

How is the investigation unfolding?

New York State Police Cpt Richard O'Brien said several separate police units were involved in the investigation, including an identification unit and a drone team.

Authorities have said they expect investigators to be at the scene for at least five days.

Police said that a phone line had been set up to help assist relatives of the victims.

The NTSB is sending a team of investigators.

The location of the intersection is said to be in a hilly region and local authorities had only recently banned large trucks from using sections of the route.