A subway train was evacuated near Dupont Station on Wednesday morning after smoke filled the cabin following a small fire at track level.

The incident happened aboard a southbound train between St. Clair West and Dupont stations at around 11 a.m.

According to TTC spokesperson Brad Ross, preliminary investigation has revealed that the train hit a metal box that usually covers a piece of safety equipment but, for reasons unknown, had been placed alongside the track following routine maintenance.

“The box for reasons we are yet to determine was left off and placed to the side and a train passing over that area clipped that box very hard – a big bang would have been heard on that train – and that caused some sparking that resulted in a wooden board over the third rail igniting slightly and smoke to smolder and get sucked into the train through its ventilation system” Ross said. “Why that happened and why the box was left where it was is something we continue to investigate.”

Ross said that a total of 21 passengers and two crew members exited the subway system through the TTC's designated Russell Hill emergency exit within about 10 minutes of the initial evacuation order being made.

No injuries were reported as a result of the fire or the evacuation but Ross said that the two TTC workers on board the train did go to hospital to be checked out for smoke inhalation.

As of 3 p.m., one of those workers had been released while the other remained in hospital for observation.

Subway trains were turning back at St. George and St. Clair West stations on Line 1 but full service resumed at around 2:20 p.m.

The resumption of service came after crews were dispatched to the scene to ensure that the track was not damaged and that signal system was functioning.