To determine the cause of yesterday's flood in downtown Montreal, the city is planning to dig up the road near the intersection of Doctor Penfield Avenue and McTavish Street.

During peak afternoon rush hour, water gushed onto the streets from a broken water main, covering a large area of the downtown core near McGill University.

City spokesman Jacques-Alain Lavallée said it's still not clear if the aging, 120-centimetre pipe was ruptured by workers in the construction zone where the water main was located, near Pine Avenue near Peel Street.

The water main is 88-years-old, according to Lavallée.

Water continues to flow near the McGill campus from a second damaged pipe, although there is significantly less than the major flooding seen Monday.

University Street remains closed between Sherbrooke Street and Pine Avenue.

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Montreal city crews worked overnight to clear the streets and re-salt streets and sidewalks. (CBC)

Workers fixed the water main break Monday evening, but crews worked overnight to clear the streets and re-salt streets and sidewalks.

Yesterday, as the water flooded onto the streets, Mayor Michael Applebaum urged residents to be careful.

"We will continue to work without stopping," he said.

McGill expects 'extensive' damage

A note sent to employees at McGill University on Monday warned of "severe flooding" on the campus grounds and inside several buildings.

"We are trying to assess damage as best we can, but it will be extensive," the note stated.

Classes are cancelled at McGill's Wilson Hall and Birks Building. Classes at the Wong Building are being relocated.

The James Administration Building was set to re-open Tuesday afternoon, and the north entrance to the McConnell Engineering Building is closed except for emergencies.

Officials are asking people to avoid the Milton Street entrance of the campus.

FACE School, an elementary and high school on University Street next to the McGill campus, is also closed.