UPDATE: This warning was lifted just after 11:30 p.m. on May 10, 2018, the same day it was issued, for most addresses in the affected area.

For more updates on this story, click here.

The original story follows below.

The City of Montreal says people within the area bounded by Bleury Street, St-Antoine Street, Beaver Hall Hill and René-Lévesque Boulevard must not use the water for any purpose.

Firefighters and Montreal's water service are on the scene investigating a possible dangerous material incident in that sector of downtown Montreal.

This is the area affected. The city is working to determine the cause of the problem. <a href="https://t.co/UKFaFNksF3">pic.twitter.com/UKFaFNksF3</a> —@CBCMontreal The city issued the notice Thursday afternoon, at the same time as firefighters began an operation at the corner of Viger and St-Alexandre streets to deal with the possible hazardous material.

About 60 firefighters were called to the multi-storey building at 445 Viger Street just after 4 p.m.

Shortly after, they located the cause of the problem: a valve on the building's cooling system had failed, which sent fluid from the air conditioning into an aqueduct.

Firefighters suspect it could be a substance used to control bacteria and prevent deposits from forming in cooling systems.

The building was evacuated. Seven people who live in the building were feeling ill, with symptoms of nausea and diarrhea. Four people were sent to hospital as a precaution.

About 60 firefighters rushed to the scene in downtown Montreal during Thursday afternoon's rush hour. (Derek Marinos/CBC)

The city says do not drink the water. Do not shower. Do not use the water for any purpose — not even if it's been boiled.

Once the water is safe to use again, the city will issue a notice.