The shooting took place in the Côte-des-Neiges neighborhood, a short drive from one of the city’s most affluent neighborhoods, Westmount. It appears to have occurred near a high-rise building with commercial units on the ground floor, including a grocery store and a restaurant.

Chief Dagher said that police arrived at the scene after receiving reports that a firearm had been seen pointing outside a hotel window. When officers arrived, he said, they were fired upon, and a gunfight ensued.

“Today, one of ours has fallen in the line of duty,” the Montreal police chief, Fady Dagher, said at an afternoon news conference. He said it had been 24 years since a police officer was last killed in the city.

The province of Quebec issued an emergency alert warning of an armed and dangerous suspect on the loose just after 12:30 p.m. It advised people to shelter in place away from windows and to lock their doors.

“My deepest condolences to the family, friends, and colleagues of the police officer who died in the line of duty,” Soraya Martinez Ferrada, the mayor of Montreal, said in a post on social media.

This is a developing story.