Service has resumed on part of the Yonge Street subway line in Toronto after severe flooding forced the shut down of a section of the system.

The subway line was closed around 1 p.m. from Osgoode station southbound to Union and from Union station north to Yonge/Bloor Station due to what appeared to be either a backed-up storm sewer or a burst sewer pipe near a construction site.

The Toronto Transit Commission announced the service was restored at around 11 p.m., well past the evening rush-hour, after crews spent hours pumping out water that flooded the tracks at Union station, which is Canada's busiest transit hub.

Earlier in the day, water was seen cascading from street level down into the station and onto the concourse and platform.

"We have a huge amount left to do," TTC CEO Andy Byford told CBC News at the time. "We've got to get this place cleaned up. We've got to finish pumping out all the water and we've got to do all of the electrical testing."

Byford was on the scene shortly after water poured through the station. He reported a foul smell.

He said the system runs on electric current and all systems, including signals, escalators and elevators must be tested for safety.

"It was like a monsoon coming down the stairs," one TTC worker told CBC News.

About 40 people were trapped on one of the streetcars in the station's flooded Harbourfront tunnel — but were eventually rescued by Toronto firefighters. The station itself was quickly evacuated.

Byford said no passengers were injured during the flood.

Mayor Rob Ford, who toured Union Station on Friday evening, praised the TTC's cleanup efforts.

"I have been on the phone with [Police Chief] Blair, offering any resources we can to help Mr. Byford deal with this terrible flood that we have had," Ford said. "I can't thank the employees and Mr. Byford [enough] for his great leadership in getting this under control."

Streetcar service has also resumed on the 509 Harbourfront and 510 Spadina streetcar lines. Both were turned away from Union station and rerouted to the tunnel servicing Queen's Quay station in the aftermath of the flood.

The road closure on Front Street at Bay Street has also cleared. Full service on the 72 Pape bus has resumed.

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