Subway service was suspended at around 11:30 on Wednesday morning between St. George and St Clair West stations after smoke started to fill the lead car on a train.
About 70 people were on the train at the time, according to the TTC's Brad Ross, and he says there were no injuries reported.
He says it appears the issue is related to a motor underneath one of the trains, but says that hasn't been confirmed.
Nothing on how long the service disruption would last.