Police emptied buildings and sealed off a large section of Montreal's downtown core for the weekend, and service was cancelled on part of one subway line after two fissures in a tunnel linking the McGill station to malls were discovered Friday.

Métro changes and alternate routes:

The risk of collapse forced authorities to close part of the downtown subway service, at least for the weekend. STM says there will be no service on the Green line between the Berri-UQAM and Lionet-Groulx stations for the weekend. The transit system will offer temporary bus service between these stations: Eastbound, on Sainte-Catherine Street. Westbound, on René-Lévesque Boulevard. The transit service also suggested riders could take the Orange line between Berri-UQAM and Lionel-Groulx stations.

"The area is closed to pedestrians as well as businesses," Montreal Mayor Gérald Tremblay said.

Fearing that roads could collapse, Montreal police cleared several city blocks of people in an area bordered by Sherbrooke, St. Catherine and Bleury streets and University Avenue, and shut the streets to traffic.

Although Tremblay had earlier said there was likely no danger to the public, engineers and city officials decided late Friday night to expand the safety perimeter and block off the widened area. Tremblay urged citizens to stay away from the cordoned-off area, which includes hundreds of shops and restaurants, over the weekend.

Bay employees first noticed crack

Problems were first spotted at about 1:30 p.m. ET Friday, when employees working in the basement of the landmark Bay department store on Maisonneuve Boulevard noticed water coming in from a section of the ceiling that had dropped a few centimetres.

Engineers were alerted to one large, seven-metre-long crack in the ceiling of an underground passageway connecting the McGill subway station, malls and The Bay. 

Firefighters were called and engineers closed one block of Maisonneuve Boulevard because of fears that the major street could collapse unless the tunnel was reinforced.

A block of Maisonneuve Boulevard was the first to be closed on Friday, after people noticed a seven-metre-long crack in the ceiling of an underground passageway connecting the McGill subway station, malls and The Bay.
(CBC)

Fire Chief Serge Tremblay told reporters about the second fissure in the tunnel later Friday night, but said experts haven't been able to conclude what caused the cracks or how long they had been there.

"It's early to say what are the risks.… Our role is to prepare for the worst and I won't say the worst will happen, but in this case, we need to make sure we are well prepared," he said.

The part of the subway line that serves Montreal's downtown core will also remain closed indefinitely as the McGill station is below the tunnel, Tremblay said.

"There are no problems to the structures of the metro system, but the metro will remain closed until further notice."

No injuries have been reported.

Closure comes amid infrastructure concerns

The CBC's Nancy Wood, reporting from Montreal, said emergency crews wouldn't risk keeping the area open in light of Quebec's infrastructure problems. The collapse of an overpass in Laval in 2006 killed five people.

"They don't take any chances," Wood said. "If they think there is the possibility of something collapsing, they're just going to shut it down for public safety.

"That's what the firefighters are telling us. They have no idea how likely a collapse is, but it's just not worth taking the risk of leaving it open."

City engineers are examining the site and trying to determine if the problem lies in the 100-year-old pipes that lie about five metres below ground level and about five metres above the McGill metro station, where The Bay is located, Wood said.

With files from the Canadian Press