Laval, Canada: At least two children were killed Wednesday when a bus rammed into a day care center in a suburb of Montreal, police said, adding that the driver had been arrested on suspicion of homicide.

The other six children transported to hospital "are out of danger," said Erika Landry, a police spokeswoman in Laval, where the day care is located.

"The driver, a 51-year-old man, was arrested for homicide and dangerous driving," she told reporters at the scene.

Canadian police did not immediately confirm the cause of the crash, which left several children trapped under the vehicle after it slammed into the building at around 8:30 am (1330 GMT).

"I helped subdue the driver who got off the bus," one father told Radio Canada, crying. His wife said the man was "half undressed" and both saw him "ram deliberately into the daycare."

"I'm devastated. We all are," Prime Minister Justin Trudeau said. "Obviously, we're all hoping and praying that the kids are all right, or that they pull through and get well soon.

"(I) can't imagine what the families are going through. But obviously, if there's anything the federal government can do, (it) will be there."

Images of the scene showed the bus smashed into a side of the building which is not located near the road but near a parking lot. Part of the roof collapsed on top of the front of the vehicle.

"We count at the moment eight seriously injured," emergency services official Marianne Lessard told AFP, even as rescue operations continued.

A large perimeter was deployed around the partly destroyed building, police in the suburban city of Laval, where the day care is located, told AFP.

Another mother, holding her own child, said it was the center's class of oldest children that was hit.

"It's a shock, a lot of parents are panicking because they can't get in, and their children are in there," she added.

'Terrible tragedy'

Victims were taken to Sainte-Justine hospital, which confirmed several were severely injured. The hospital was set to have a press conference later in the day.

"What a terrible tragedy this morning in Laval," Quebec Premier Francois Legault tweeted.

"There is nothing worse than being afraid for your child. I am thinking of the children, the parents and the employees," he added.

"As a father, I am shaken," he said later at a press conference.

"I can understand the anguish that the parents are going through," he said.

"I am shocked by this news. The investigation continues to understand this tragic series of events," tweeted Stephane Boyer, the mayor of Laval, the third-largest city in Quebec.

"All of my support to the parents at these difficult moments," he added, saying he was going to the scene to meet with the families.

"Laval is wholeheartedly with you and will be there for you."