A fire swept through an apartment complex for the elderly in the small Quebec town of L’Isle-Verte early Thursday, killing at least five and leaving roughly 30 others unaccounted for, police said.

Frigid temperatures have made search efforts difficult, police Lt. Guy Lapointe said hours after the fire began. Water used to fight the blaze has frozen into ice, he said, trapping pockets of fire, and possibly victims, in the collapsed three-story building.

Police said they fear some of the missing were in the burned and frozen remains of the 52-unit Residence du Havre, situated in the town of about 1,400 people near the St. Lawrence River northeast of Quebec City.

About 20 people escaped — some were taken to a hospital, and others to a nearby school.

Authorities were still struggling to figure out exactly how many people were in the building when the fire hit.

Emergency personnel worked in temperatures well below freezing. The temperature in nearby Riviere-du-Loup was -22 C (-7 F) at 7 a.m. ET, according to Environment Canada.