A massive water main break along Crowchild Trail has been repaired and the city expects the southbound lanes to reopen early Tuesday morning.

A serious water main break late Saturday night in the city's southwest shut down a section of Crowchild Trail.

Southbound lanes from Bow Trail to 33rd Avenue on Crowchild Trail are closed to the general public, with one lane restricted to local residents, transit and emergency vehicles only.

'This water main break is one of the largest the City of Calgary has ever experienced.' — City of Calgary

City crews worked through the night Sunday tearing up all three southbound lanes between 32nd and 33rd avenues southwest.

A new pipe has been placed and tested, crews are working to fill and repave the excavated area Monday night.

The city expects the work to be done in time to open the southbound lanes on the major commuter route by 5 a.m. MT Tuesday.

"Initially crews found that a 600-millimetre section of pipe had burst. A crack has since been discovered that runs from the break, putting the total length at six metres. The excavation was complicated by the discovery of an abandoned ATCO gas line that had to be removed by ATCO," said the city in a release.

"This water main break is one of the largest the City of Calgary has ever experienced. The 400-millimetre water main is cast iron and was installed in the 1930s."

An estimated 50,000 commuters are affected by the closure.

Calgary Transit says while transit is running, delays are expected for routes 18, 20, 112 and 181. Transit riders are being advised to allow extra time for travel, and southbound commuters are being asked to find alternative routes.

Sean Somers, with the city's roads department, says they are working to ease the congestion on alternate routes.

"We're adjusting some of the signal timings on the other major routes around the area to try [and] increase flow into the downtown core in the morning and out of the downtown core in the afternoon," he said.

"So the message for us here really today is this is unfortunate this has happened, but it has."

Crews to work on unrelated rupture

City crews were also dealing with another unrelated water main break at 19th Street and 28th Avenue S.W. that left roughly 40 homes with no water Sunday.

Water wagons have been dispatched to the homes in the Marda Loop area, and the city says it plans to make repairs Monday morning.