A Montreal police officer and a civilian were killed after a gunman armed with a long gun opened fire in the city's Côte-des-Neiges neighbourhood, police said, in an attack the police chief described as a nightmare and the first line-of-duty killing of a Montreal officer in 24 years.

The suspect was killed by return fire after officers were targeted at the scene, according to police. A second officer was seriously injured but is in stable condition, police chief Fady Dagher said.

Emergency services received a call at about 11:35 a.m. reporting a person pointing a gun out of a window at the Hilton hotel, Dagher said. Officers who arrived were met with gunfire, he said, and video footage indicated the shooter was also outside the hotel.

The officer killed was identified as Constable Mohamed Lamine Benredouane, 34, who had been with the force since 2021. CBC News reported the civilian killed as Michael Mizrahi. A second civilian sustained minor injuries, according to CBC.

Dagher said he did not know who had fired the shot that killed the civilian.

"It's a very, very sad day. It's a nightmare," Dagher told reporters, adding that it was the first time in 24 years a Montreal officer had been killed on duty. Such shootings in the city are rare.

The shooting took place in a partly Jewish neighbourhood that includes kosher markets and restaurants, but police declined to comment on a possible motive.

Videos posted to social media appeared to show an exchange of gunfire between police and a person carrying a long gun and wearing an olive-coloured jacket and cargo pants. The footage appeared to show a civilian and at least one officer being struck, while the person in the olive clothing appeared to be shot while adjusting or reloading the weapon. CBC said it had verified video in which at least 29 gunshots could be heard.

Prime Minister Mark Carney said he was horrified by the violence.