A 15-year-old boy was seriously injured after falling from the top of a moving GO train yesterday.

For its part, the police said that four teenagers aged between 14 and 16 boarded a train heading east at Union Station just before midnight, and as it was moving, three of them climbed onto the roof of the train.

At one point, the 15-year-old boy struck a stationary object near Danforth GO Station and fell, a police source told 680 News Radio Toronto that the other teenagers returned to the train to call 911.

The paramedics also transported the 15-year-old boy to the hospital with serious injuries, and he is still in a life-threatening condition.

The police did not mention whether any charges are pending as the investigation is ongoing.

Metrolinx said in a statement: “Such incidents are often tragic and life-changing, and we urge everyone not to take this dangerous action."

It added: “Our thoughts are with the boy's loved ones and all those affected, including our team members and first responders, and Metrolinx is working with local law enforcement authorities to investigate this extremely serious incident."