Toronto: An Indian couple visiting Canada and their three-month-old grandchild were among four people killed on the spot in a multi-vehicle collision when Ontario police pursued a liquor store robbery suspect driving the wrong way.

All four people were pronounced dead at the scene on Highway 401 in Whitby, about 50 kilometres east of Toronto, police said on Thursday.

Ontario's Special Investigations Unit (SIU) said that two of the victims, a 60-year-old man and a 55-year-old woman, were visiting from India. However, the SIU did not release the names of the victims.

The couple's three-month-old grandson also died in the multi-vehicle collision. Highway 401 was closed for several hours after the incident on Monday, it said.

The agency said that the parents of the infant, his 33-year-old father and 27-year-old mother, were travelling in the same vehicle and were taken to hospital.

The mother's injuries are serious, the SIU said.

The 21-year-old robbery suspect was also killed in the collision, which involved at least six vehicles, CBC News reported.

Officials have said the deadly car chase started with a liquor store robbery in Bowmanville and ended around 20 minutes later after the suspect in a cargo van led Durham police on a high-speed chase against opposing traffic on Highway 401.

A 38-year-old male passenger from the cargo van was also taken to the hospital to be treated for serious injuries.

The autopsies for the victims were conducted in Toronto on Wednesday.

Seven investigators, one forensic investigator and one collision reconstructionist continue to investigate this case, the statement said.

The SIU is an agency called in to investigate whenever police are involved in a death, serious injury or allegations of sexual assault.

Milica Maljkovic Birkett, a witness to the deadly police chase and had a lucky escape, said she didn't have time to think.

She was driving her regular commute on the 401 when she was suddenly face-to-face with the suspect van barrelling toward her car on the wrong way.

"I was like, 'Oh my God, like what just happened? What's going on?'" Maljkovic Birkett told CBC Toronto on Thursday.

Maljkovic Birkett said the experience has taken time to process.

"It's so scary," she said. "For whatever reason, somehow my life was spared. But (four) others were taken and that was just really heavy," she said.