Montreal's Métro was fully operational again and most downtown streets were reopened in time for Monday morning's rush hour after crews worked non-stop on the weekend to shore up the ceiling of a pedestrian tunnel that was at risk of collapsing.

City officials cordoned off a seven-block perimeter of the downtown core on Friday, closed part of the Métro's Green Line and evacuated buildings while they investigated two cracks running the length of a city block.

Engineers and city employees survey the streets around The Bay department store in Montreal on Saturday.
(Peter McCabe/Canadian Press)

Workers then installed about 1,000 metal posts under the concrete slab over the tunnel, which links the McGill station to the Bay department store and malls.

Mayor Gérard Tremblay told a news conference Sunday night that businesses in the zone may now reopen and six train stations along the Green Line were back in operation.

The only stretch of road still closed to vehicles on Monday is de Maisonneuve Boulevard, from Aylmer Street to Union Avenue.

The concrete ceiling had dropped about 2½ centimetres, but Tremblay said there is no longer any risk of a collapse.

The security perimeter had left dozens of retail businesses closed during the busy back-to-school shopping period.

The fissures were discovered during a summer of heightened anxiety over the province's aging infrastructure.

Inspections and hearings over crumbling roadways have been on the minds of Quebecers and the agendas of politicians.

Last September, an overpass in neighbouring Laval collapsed on a highway, killing five motorists and injuring six others.

With files from the Canadian Press