TORONTO — A busy section of Toronto’s downtown subway line remains closed during this morning’s rush hour, due to what the transit agency is calling an “environmental spill.”

The Toronto Transit Commission says the north-south line (Line 1) remains closed between Bloor-Yonge and Union stations due to the spill at College Station.

It says about 70 buses are being used to shuttle passengers around the closure.

Emergency crews are on the scene, and the transit commission says they are working to determine the source of the spill.

Once the spill is identified and cleared, it says work crews will be sent in to make any needed repairs.

There’s no immediate word on when service will be restored but commuters are being advised to take alternate routes.

TTC CEO Andy Byford says the problem began Monday night when a staff member noticed a substance leaking through a tunnel near College Station.

“We always put safety first,” said Byford. “We stopped service to have a look and see what it is.”

“The substance smells like gasoline,” he added. “So we cannot take any chances with this because obviously, running an electric train service, trains create sparks. All night we’ve been doing tests on the substance _ it’s not water and we’ve been pumping it out.”

Byford says crews are searching for the where the leak originated and then must cap it off.

“I appreciate customers won’t be happy about this,” he said. “I’m not happy but what can you do? If it’s gasoline there is no way you can run an electric train service.”