(CNN) -- Search teams combed ice-covered debris for dozens of elderly people reported missing in the aftermath of a fire at a senior retirement complex in a small town in Canada's Quebec province, a police official said Friday.
At least eight people died in the fire that swept through the Residence du Havre in L'Isle-Verte, said Lt. Guy Lapointe, a police spokesman. Up to 30 people are missing, he said.
Frigid temperatures have made search efforts difficult, Lapointe said. Water used to fight the blaze froze, coating the collapsed three-story building in ice.
Lapointe said it was unknown how long it will take to complete the search.
"The cold is extreme, the equipment could freeze, we could run into other issues, so at this point it's really difficult for me to set a timetable of any kind," he told CNN affiliate CTV.
Robert Berube's mother was among the missing, he told CTV.
"My mother, she's blind," he said. "She's still there... I can't believe it... I don't know how to handle it."
Authorities have not said what caused the fire that began early Thursday morning at the complex, where at least 52 people were believed to be living. At least 37 of the residents are older than 85, according to government documents obtained by CNN affiliate CBC.
Acting Mayor Ginette Caron told CBC that many of the residents had Alzheimer's disease and used wheelchairs or walkers.
Witnesses said they saw a number of residents calling out to firefighters from their windows and balconies for help.
Pascal Fillion, who lives near the complex, told CTV he heard screams coming from inside, but the fire was so intense there was little firefighters could do.
"There was one person we saw, who they wanted to save, but he was on the top floor, and with the fire and the wind they weren't able to come any closer," he said.
CNN's Maria P. White contributed to this report.