A woman was killed and part of a man's leg was amputated after a driver slammed into pedestrians and crashed into a former restaurant patio in Burlington, Ont., on Saturday morning, Halton police said.

The original call came in shortly after 10 a.m., police said. Multiple witnesses called saying they saw a man driving erratically on Fairview Street, said Insp. Derek Davis.

"Not staying in its lane, driving in an unexpected manner," said Davis, who said the curious driving was first reported "well west" of the crash scene.

At one point, the driver reportedly left the roadway, drove onto the sidewalk and struck a 19-year-old male pedestrian. The man's leg was amputated below the knee and he was airlifted to Hamilton Health Sciences Centre with life-threatening injuries, police said.

The driver of the SUV was also taken to hospital with injuries after he crashed into the patio of a now-shuttered restaurant. (Michael Cole/CBC)

The driver then continued on Fairview Street before striking a 58-year-old woman, who was standing nearby in front of the now-closed restaurant, Chaps. The woman was pronounced dead at the scene.

The vehicle came to a stop after the driver crashed into the former restaurant's patio.

Driver believed to be in 70s

The driver is a man believed to be in his 70s. Police said he sustained head injuries and was transported to hospital by ambulance.

"What caused the erratic behaviour is still under investigation," said acting Sgt. Tom Zafiridis. "The driver may have suffered a medical episode, which may have contributed to the accident itself."

Earlier on Saturday, Davis said police are "open to all possibilities, whether it is impairment, whether it's some sort of a crime in progress, a medical issue."

"We don't have a definitive answer at this time, but we've certainly not ruled any possibility out."

Inspector Derek Davis says police are still investigating the cause of the collision. (CBC)

The 19-year-old victim is still in hospital in serious condition, said Zafiridis on Saturday afternoon. He said he believes the driver and two victims are all from Burlington.

Police are still investigating how far the man had been driving and where, he said.

The Halton police traffic reconstruction unit is investigating the series of collisions.

Anyone with potentially valuable information is asked to contact the Halton Regional Police Service or leave an anonymous tip with Crime Stoppers.