A 19-year-old woman has died in hospital after she was struck by a vehicle on the Gardiner Expressway early Monday morning, Toronto police say.

Police said the woman was a passenger in a Toyota Corolla, but somehow exited the car and wound up on the road, where she was hit by a truck in the eastbound lanes, just west of Dufferin Street, police said.

The incident occurred at about 2:30 a.m.

Paramedics rushed the woman to a trauma centre, where she underwent emergency treatment for life-threatening injuries. She died of those injuries several hours later. The woman's name hasn't been released.

Because of the severity of the crash, police closed the Gardiner's eastbound lanes between Jameson and Spadina avenues to conduct an investigation at the scene. The lanes reopened at 8 a.m.

The drivers of the vehicles involved in the incident remained at the scene.

Police said a 23-year-old woman was behind the wheel of the Corolla, while a 40-year-old man was driving the truck.

As they investigating the circumstances of the collision, police are trying to figure out how the woman exited the vehicle. No charges have been laid.

Anyone with information is asked to call police at 416-808-1900 or Crime Stoppers anonymously at 416-222-TIPS (8477).

@ChrisKitching is on Twitter. Don't forget, for instant breaking news follow @CP24 on Twitter.