A notice to Toronto commuters and pedestrians who happen to be in the downtown core tonight: Don't be alarmed by the huge presence of emergency responders at Union Station starting late this evening and into the early hours Sunday morning.
It's all part of the largest ever multi-agency emergency exercise simulation at Union Station.
It will involve first responders and more than 150 volunteers.
It's part of a "worst-case scenario" training exercise that is being coordinated with the City of Toronto, Toronto Police Services and Paramedics, as well as Toronto Fire Services.
It's intended to test the response to a “multi-casualty event in a large complex environment.”
Metrolinx spokesperson Anne Marie Aikins tells The Toronto Star, "The simulation which will involve an assailant with an automatic weapon, a fire on the train platform, 150 volunteer actors and multiple casualties will be the largest, most complex exercise ever held at Union Station."
Some of the actors will be pretending to be seriously injured or in distress. There may also be smoke at platform level.
Metrolinx issued the following statement on their Twitter account:

TWITTER/@Metrolinx
Metrolinx goes on to tell the Star that they want to notify the public about the emergency exercise in order to reduce the number of "concerned 911 calls".
There will be no impact to public transit, but Metrolinx saying in a tweet that there will be some road/sidewalk diversions.
The northbound lanes of York Street, from Bremner to Front Street and sidewalks and eastbound lanes of Front Street, from York Street to Bay Street will be closed during the exercise.
With files from The Toronto Star