A York Regional Police officer tried to stop an SUV driven by a 13-year-old a short time before the vehicle was involved in a crash that left a 13-year-old passenger with "life-altering injuries" according to the province's police watchdog.

According to the Special Investigations Unit (SIU), a York Regional Police officer spotted the vehicle in the area of Dufferin Street and Centre Street in Thornhill at around 4:40 a.m. this morning.

When the officer attempted to stop the SUV, the driver fled the scene, the SIU said in a release.

About 20 minutes later at 5 a.m., the vehicle collided with a fuel truck near Finch Avenue West and Dufferin Street in North York.

The underage driver then lost control of the SUV, spun out, and came into contact with a GO Transit bus, which was stopped at the intersection.

The passenger of the SUV, who police say sustained “severe” injuries, was taken to a trauma centre for treatment.

“I believe right now he is currently in surgery at the hospital. By the level of injury I have heard, it is going to be a serious, life-altering injury that he has sustained,” Sgt. Murray Campbell told reporters at the scene.

The teen driving the vehicle has been taken into police custody but officers have not said what charges he may be facing.

“We are looking into how they came into possession of this vehicle. Obviously two 13-year-olds should not be driving or in possession of a motor-vehicle,” Campbell said.

A man, who identified himself as the father of the hospitalized teen, said the vehicle the boys were driving belonged to him.

He said he last saw his son at their home in the Jane and Finch area at midnight but fell asleep a short time later.

He had left the keys to the vehicle in his jacket, he added.

“The next thing I know the hospital is calling saying he is in emergency,” the man told reporters at the scene on Tuesday morning.

He said his son’s surgery was expected to last 6.5 hours and doctors are trying to save the boy’s leg.

The man said he does not believe his son has ever taken his vehicle before and noted that he does not know the 13-year-old boy who was driving.

The collision reconstruction spent hours gathering evidence at the scene Tuesday.

“Witnesses have explained to us that the (SUV) was travelling at an excessive rate of speed and might have been travelling through red lights prior to the collision,” Campbell said.

“We are asking if anybody was in the area (and) has any dash cam footage that may be able to show a path of travel that would be very, very helpful for us.”

The SIU said Tuesday afternoon that they are investigating the incident and have assigned three investigators and two forensic investigators to the case.

The SIU is an arm's length agency called in to investigate whenever police are involved in an incident that results in a death, serious injury or allegations of sexual assault.

The intersection of Dufferin Street and Finch Avenue was closed for several hours while police investigated the crash. It reopened at around 5:30 p.m.