Metrolinx spokesperson Anne-Marie Aikins said police are investigating after a man believed to be in his 30s was hit by a Barrie-bound train and killed.
Toronto paramedics said the man was pronounced dead at the scene.
It's not clear how the man was struck by the train. In a tweet, GO Transit called it a "tragic accident" and Aikins said it's believed the man didn't intentionally jump in front of the train.
There are delays on the following train lines as of 7:30 p.m.:-
Aikins said a number of platforms at Union Station are closed and some trains are being re-routed.
For more updates from GO Transit, check here.