MONTREAL — Montreal police have taken over an investigation into a building fire that has forced the complete closure of the Jacques Cartier Bridge, a major span to the city’s South Shore.

A vacant industrial building on the Montreal side of the bridge caught fire Tuesday, with firefighters called to the scene around 11:30 p.m. at the intersection of De Lorimier Avenue and Logan Street. The fire started on the first floor of the three-storey building and spread to the upper floors.

Officials with the Jacques Cartier and Champlain Bridges Incorporated — the federal corporation that manages the bridge — shut down the span to traffic on Wednesday at 6 a.m. because smoke from the fire was thick and they feared the building would collapse onto the span’s pillars.

Montreal police spokeswoman Const. Jeanne Drouin said Wednesday that the arson unit had not accessed the scene. Authorities said they didn’t know whether anyone was inside the building at the time of fire.

"For now, what I can tell you is that we are truly investigating a fire of an undetermined nature," Drouin told reporters.

Montreal fire department division chief Martin Guilbault said the fire was under control later on Wednesday morning and excavators had arrived on site to knock down the building.

"The advertising panels on the roof of the building are our biggest concern right now," Guilbault said.

Guilbault said engineers from the federal bridge authority were assessing the structure and once they give the go-ahead, the southbound lanes should reopen. It was too early to say around noon what the impact would be on the evening rush hour.

"The next steps are to work on demolishing the building, and as soon as we’re sure the structure is safe, we’ll reopen the (bridge) lanes," Guilbault said.

The bridge, he said, is a "major artery in the city of Montreal. We’re doing everything we can to reopen it as quickly as possible. However, we have to do it safely and make sure we don’t damage the bridge."

The building at the foot of the bridge was constructed in 1910 and its location forced the bridge’s architect to design a curve in the span to snake around the structure, according to Heritage Montreal. The building was first occupied by soap manufacturer Joseph Barsalou and it was later occupied by other companies including Procter & Gamble and pharmaceutical firm Familex. It has been vacant for some years and the local borough was studying what to do with the site.

This report by The Canadian Press was first published Jan. 21, 2026.

Sidhartha Banerjee, The Canadian Press