A number of Canadians were injured when a double-decker bus crashed en route to Toronto from Philadelphia early Saturday morning, killing four people.

The double-decker Megabus, which is popular with travellers in the northeastern United States, had 26 passengers on board when it hit a low-hanging railroad bridge on the Onondaga Lake Parkway in Salina, a suburb of Syracuse, N.Y., around 2:30 a.m.

The driver and the injured passengers were taken to local hospitals for treatment.

Seventy-one-year-old Vicky Reed and her husband, of Dundas, Ont., were among those on the bus when it hit the bridge and flipped onto its side.

"All of a sudden there was a big crash and I fell over, was thrown over people and then it was all quiet," Reed said. "The front of the bus had been pushed back just like an accordion."

According to Reed, the four deceased passengers had been sitting on the top level of the bus, near the front, where the vehicle would have hit the bridge.

"The bus was too tall and so it sort of ripped the top of the front part of the bus off," said Reed, who suffered a knee injury. "The bus was then sort of on its side."

Richard Blansett with the Red Cross of Central New York said another Canadian couple who survived the crash was from the Toronto area.

"The damage to the bus was severe," he said. "The people inside were tossed around and injuries ensued."

Passengers suffered anything from cuts and bruises to "severe injuries" that continue to require treatment in hospital, Blansett told CTV News Channel. Many of those with minor injuries were quickly released.

Seven of 20 passengers released from hospital are from Ontario, said Don Carmichael, senior vice president of Coach USA, which operates Megabus.

Four passengers and the driver have been admitted to hospital overnight, he said. The injuries of two passengers "are considered serious."

Lisa Monette, a spokesperson for the Foreign Affairs department, said Canadian officials in Buffalo are working with local authorities to determine how many Canadians were on the bus and if any Canadians are among the dead.

Monette said any Canadians on the bus will be provided consular assistance as needed.

Onondaga County Sheriff Kevin Walsh told a local newspaper that three men and one woman were killed in the crash. According to Walsh, one of the dead was from Kansas, while two others were not from the United States, but he could not say which countries they hailed from.

A local Red Cross official said injured passengers are being treated at four different hospitals. As of early Saturday afternoon, 14 had been released and were receiving food and other aid at a downtown Syracuse hotel.

Carmichael travelled to the scene Saturday and said the company will conduct a full investigation.

According to Carmichael, the bus was not on its route when it crashed.

"It is not an alternative route prescribed, that's going to be part of our investigation," Carmichael said. "We really have no idea why it was on that route."

The driver of the bus has reportedly been able to speak with investigators despite his injuries.

The bus left Philadelphia at 10 p.m. Friday and was scheduled to stop in Syracuse and Buffalo before arriving in Toronto.

Megabus.com, which launched in April 2006, touts itself as the "first, low-cost express bus service to offer city-to-city travel for as low as $1 via the Internet." The company says it services 28 major cities in the U.S. Midwest and northeast.

The company was introduced in Canada in August 2009, and travels between Toronto, Kingston and Montreal.

Carmichael said the company prides itself on its safety record.

"We have extremely high standards of safety and we've transported in excess of 7 million people and never an incident like this," he said.

"The company's thoughts and prayers are with the passengers and the relatives and loved ones of those passengers who have lost their lives."

With files from The Canadian Press