Four people have been taken to hospital and at least 15 others were injured after a double-decker Megabus and a tractor trailer collided on Highway 401 near Lancaster, Ont., on Tuesday afternoon.

In a statement, Megabus confirmed that one of their vehicles travelling to Kingston, Ont., from Montreal was involved in the collision at approximately 2:30 p.m. The bus was carrying 45 people.

Bus crash near Lancaster, Ont.

One woman, who was listening to music at the time of the crash, said the impact sent her flying across the bus.

"All of the sudden the bus stops … and I don't know what happened. I flew to the other side of the bus," the woman told CTV Ottawa.

"Someone caught me so I was OK," she added.

Another man, who was sitting on the second floor of the bus, said that passengers sitting on the lower level were hit the hardest during the collision.

"Everybody up there more or less was OK, but when we went down, the front of the bus was crushed and there were more serious injuries," said the man.

The tractor trailer’s driver, Ishamael Mohammed, said the incident left him stunned.

"Some people from the bus came out and tried to pull out (people with injuries). I was in shock … I just came out and I was just looking, I was trying to control myself because I was very shocked," said Mohammed, who drives for Caravan Trucking.

Bus crash near Lancaster, Ont.

Another bus arrived to transport non-injured passengers away from the scene.

Fire Chief Vic Leroux, from the nearby township of South Glengarry, told CTV News Channel that the passengers were evacuated to a Williamstown arena.

The westbound lanes of Highway 401 have been closed as the investigation continues.

Megabus said in the statement that it is "fully co-operating" with authorities during their investigation.

Lancaster, Ont., is located just east of Cornwall, Ont., and about 125 kilometres southeast of Ottawa.

With a report from CTV Ottawa