A backpack holding a noxious substance forced Winnipeg emergency officials to close down part of a road near the Health Sciences Centre this morning.

Deputy fire chief Bill Clark says the white substance was found when security officials in the hospital's emergency waiting room checked a man's backpack.

Hospital staff found the man in another area of the hospital and thought he needed help.

When security officers opened the man's bag, a noxious odour came from the bag as soon as it was opened, Clark said.

What the substance is remains unknown, but emergency action had to be taken since it could have put patients and staff in danger, he added.

"We don't know whether there's real risk or not," he told CBC News on Saturday.

"We treat it as we know it to be and we'll engage with it [the substance] expecting the worst, based on what we know."

The individual was assessed by medical staff, decontaminated of the substance, and then detained. No one was hurt in the incident.

A portion of William Avenue between Sherbrook Street and Tecumseh Street was closed for much of Saturday morning, but has now been reopened.