Ontario's police watchdog is investigating after a vehicle collided with a TTC bus during a police pursuit Saturday in north Toronto.

A man and woman in the vehicle were taken to hospital with serious injuries, the SIU says.

An Ontario Provincial Police officer saw two vehicles driving at a high speed on Highway 401, near Leslie Street, Saturday morning, the SIU says, according to "preliminary information."

The officer started following one of the vehicles as it took the Bathurst Street exit, it said.

The vehicle crashed into a TTC bus around Keele Street and Sheppard Avenue, the SIU says.

2 people in 20s seriously hurt

A 23-year-old man and 24-year-old woman were thrown from the vehicle and seriously injured, the agency said. They were taken to hospital.

The SIU is looking for witnesses and urging anybody with information to contact the lead investigator at 1-800-787-8529. Anyone with video footage can upload it through the SIU website.

The SIU is an independent agency that investigates incidents involving police where someone is injured, sexually assaulted or killed.

The SIU says three investigators, two forensic investigators and a collision reconstructionist have been assigned to the case. One subject officer and two witness officers have been designated, it said.