A girl is in life-threatening condition after she was thrown from a vehicle following a crash on Highway 401 in Mississauga.

Police say a car and a transport truck heading eastbound collided. The car then rolled over onto the shoulder.

That's when the girl was ejected from the car.

The four-year-old girl was taken to hospital. She suffered life-threatening injuries. Another child in the vehicle, a two-year-old girl, was also taken to hospital but did not suffer any injuries.

The driver of that vehicle was also taken to hospital with minor injuries.

“The transport truck driver remains on scene as she is not injured at all, and has been speaking to officers now,” says Sgt. Kerry Schmidt in a video posted to his Twitter account.

It’s not clear what caused the crash or whether any charges are expected.

All of the eastbound lanes were closed at Winston Churchill Boulevard while police investigated. Westbound traffic was also moving very slowly because of the visual distraction combined with rush hour traffic.

Schmidt says he hoped that the eastbound lanes would be reopened within a few hours. At 5:39 p.m., he posted an update saying that the eastbound lanes would be opened in the coming minutes.

Traffic was reportedly backed up as far back as Milton and beyond.

Drivers are advised to take a different route while traffic remains congested.