A water main break flooded King Street and Forsyth Avenue near McMaster University and sent water flowing into the underground parking garage at the McMaster Children's Hospital late Monday afternoon.

City crews had stopped the flooding water and were preparing to repair by 6:30 p.m. Monday. The university said traffic was being diverted to other parking lots.

There's been no disruption for patients at the hospital, said Hamilton Health Sciences spokesman Tom Perry. The entrance to the emergency department is not affected by the flooding, he said.

The number of homes flooded wasn't available, as not everyone was home yet, the city's interim water director, Mark Bainbridge, said. Water access was shut off to a handful of residences while the pipe was being isolated, he said.

Fire crews were going through the garage to make sure there were no people left inside. The water in the garage was between 15 and 45 centimetres deep, said Hamilton fire spokesman Claudio Mostacci.

Forsyth Avenue at King Street remained shut down while the repairs continued.

Repair to take between seven and 12 hours

The break came in a 500-millimetre pipe on Forsyth Avenue between King and Arnold streets, said Jasmine Graham, a city spokeswoman.

The city crews were working around 5:30 p.m. to isolate the leak and preparing the area to excavate so the water main break could be fixed.

After the leak is stopped, the garage will have to be pumped out.

Hamilton Water estimates the repair will take between seven and 12 hours, Graham said, so the work should be finished before most campus activity kicks off Tuesday morning.

A main break on a cold night

Temperatures are expected to be well below freezing Monday night.

Graham said salters and sanders have been notified of the water main break and should be on scene when the repair is complete to make the streets passable for pedestrians and vehicles.

Bainbridge said an area of road about 150 metres long was covered in water at some point. But he said the water has been draining away since the source of the leak was found.

"I wouldn't characterize it as completely ice-free, but I don't think it's causing any real problems," Bainbridge said.

'Exams are proceeding as scheduled'

The university said that the flooding did not impact university buildings.

"McMaster remains open as usual," the university said. "Exams are also proceeding as scheduled."

There is water supply to campus, the university said.

Water from a burst water main is pouring down into the parking garage beneath McMaster Children's Hospital at the corner of Forsyth and King West. (Dave Ritchie)

Water main break at King and Forsyth. McMaster staff directing visitors around campus to other lots. —@McMasterU

Watermain break at King and Forsyth. <a href="https://twitter.com/hashtag/HamOnt?src=hash">#HamOnt</a> (🎥: <a href="https://twitter.com/JMonacoBarnes">@JMonacoBarnes</a>) <a href="https://t.co/dGjDJDWIbM">pic.twitter.com/dGjDJDWIbM</a> —@theSilhouette

Free hospital parking today!! <a href="https://twitter.com/hashtag/McMaster?src=hash">#McMaster</a> <a href="https://twitter.com/hashtag/Flood?src=hash">#Flood</a> <a href="https://twitter.com/hashtag/HamOnt?src=hash">#HamOnt</a> <a href="https://t.co/T8BoIkFkm0">pic.twitter.com/T8BoIkFkm0</a> —@DaveyD99