Everything we know about the horror limo crash that killed 20 people.

A limo full of people – including two newlywed couples – on their way to a birthday celebration in upstate New York were killed in a horror crash on Saturday afternoon.

The limousine driver and 17 passengers, as well as two bystanders, were killed when the driver failed to stop at an intersection and ploughed into a parked 4WD in a carpark at Apple Barrel Country Store and Cafe in Schoharie.

The crash, which also killed two bystanders near the unmanned four-wheel drive, is the deadliest US transportation accident in almost a decade.

According to an aunt of several victims, the guests were celebrating a 30th birthday. Earlier reports incorrectly said the guests had been to a wedding.

Several victims have been identified

While authorities haven't released any of the crash victims' names, several have been identified by family and friends through interviews, social media and fundraising sites.

Barbara Douglas told the New York Post that her niece, Amy Steenburg, was married in June and the limo ride was part of a surprise for her 30th birthday.

Her husband Axel, was also killed in the crash, as well as his brother Rich Steenburg. Amy's three sisters - Abigail Jackson, Mary Dyson, Allison King - and their husbands also perished.

"They were beautiful girls, full of life. They had their whole lives ahead of them," Barbara said.

At least two little girls will grow up without parents as a result of Saturday's tragedy. Abigail Jackson and her husband Adam were parents of four-year-old Archer and 16-month-old Elle.

On a GoFundMe page to raise money towards a college fund for Archer and Elle, family friend Sarah Maltzman said the Jacksons were "amazing parents to these girls and taken much too soon".

"While families will step in and provide loving care for these girls, there will be expenses that we can help with during this time when we otherwise feel so helpless."

Two other victims were Erin, 34, and Shane McGowan, who also married in June.

Erin's father Anthony Vertucci shared a message of heartbreak on Facebook.

"My heart has stopped. Unspeakable tragedy that I can't comprehend and will never come to terms with," he wrote next to a photo of his daughter on her wedding day.

"I just wanted all of you to see pictures of Erin and Shane, these two beautiful and amazing people, on the best and happiest days of their lives."

The disturbing crash scene

It's not yet known whether driver error or a mechanical fault caused the limo to run the stop sign and crash.

The 2001 Ford Excursion limousine was travelling southwest on Route 30 in Schoharie, about 270km north of New York City around 2pm when it failed to stop at a T-junction with state Route 30A, State Police First Deputy Superintendent Christopher Fiore said at a news conference.

Witnesses reporting bodies on the ground and broken tree limbs everywhere.

The crash "sounded like an explosion," said Linda Riley, of nearby Schenectady, who was on a shopping trip with her sisters and had been in their parked car at the time at the store.

When she got out of her vehicle, she saw a body on the ground, she said. People started screaming.

The National Transportation Safety Board is investigating, said its chairman, Robert Sumwalt.

"This is one of the biggest losses of life that we've seen in a long, long time," he said, the deadliest since February 2009 when Colgan Air Flight 3407 crashed in Buffalo, New York, killing 50 people.

New York governor Andrew Cuomo said state police were working with federal and local authorities to investigate the crash.

-With AAP