The incident at the wholesale grocery store, which injured a total of six people, sparked panic among shoppers, many of whom rushed to help those who had been mowed down by the vehicle, witnesses said.
Tracy Carne was leaving the store just moments before the crash took place around 12 p.m., and remembers hearing a loud roar from a red, four-door sedan.
"We just hear the rev, like an unbelievable rev, and then boom — a complete explosion. And then the glass, it was like a waterfall of glass," she told local radio station BlackBurnNews.com.
Carne said she and a friend were standing right behind a woman and two young girls who were thrown into the air after being hit by the car.
"I pulled my phone out and called 911," she said, struggling to control her emotions. "I need to know if the girls are ok."
Carne added that a woman was driving the driver of the car that reversed into the store's front doors.
Araam Wendy, a Costco employee, ran out after hearing the crash and started ushering bystanders away from the shattered glass that littered the ground.
"There was just blood everywhere, the lobby's full of blood and shattered glass. Everyone was in panic," he told BlackBurnNews.com.
"There was a four year old who was severely bleeding and then you had the 10- or nine-year old daughter who was knocked out cold, and then you had the unconscious pregnant woman, the mother, who was also knocked out."
Police said a woman and her two children were in critical condition following the crash, but would not confirm eyewitness reports that the woman was pregnant. An investigation is underway and charges are pending, police said.
The car which rammed into the store remained on scene Friday afternoon.
"Members of the traffic management unit are there doing accident reconstruction so it will likely remain there until that is completed," said Const. Alanna Hollywood.
"The Costco is currently closed to the public while the investigation is continuing."
The area around the store was cordoned off by police tape in the aftermath of the crash. Shopping carts were used to block off the Costco's front doors.
_ By Diana Mehta in Toronto.