Police said that five people died and about 30 were unaccounted for after the early morning blaze ripped through the Residence du Havre in the small community of L'Isle-Verte, about 230 km northeast of Quebec City.
A police official said severely cold weather was making working conditions difficult, and he did not know how soon police would be able to update the death toll.
"So many things could happen that we can't plan on - the cold is extreme, the equipment could freeze, we could run into other issues," said Guy Lapointe, spokesman for police in the eastern province of Quebec.
The ice formed after firefighters, working in temperatures that dropped as low as 22 Celsius, spent many hours dousing the building with water. In some cases the resulting ice is 30 to 60 cm thick.
"The method that we're using now with regards to melting the ice is we're using steam," Lapointe said.
"The steam is being used for us to be able to advance at the scene, being able to preserve the integrity of potential victims."
The cold was so intense that teams of police, firefighters and coroner's office officials could only work in 45-minute shifts.
Police have not managed to track down all the residents who might have been in the building, and Lapointe said it is possible that nonresidents had been in the building.
Officials said they do not know what caused the fire and Lapointe appealed to local residents to provide any videos or pictures they may have taken after the fire started shortly after Wednesday midnight (local time).
