A fire raged through an old people's home in eastern Quebec, trapping residents dependent on wheelchairs, leaving five dead and around 30 missing.
Ca nada's prime minister Stephen Harper warned there is little doubt the death toll will be high.
Officials said firefighters saw and heard people in the building that they were unable to save.
Many of those unaccounted for were confined to wheelchairs and walkers and only five residents in the centre were fully able to care for themselves, said Ginette Caron, acting mayor of the small town of L'Isle-Verte, about 140 miles from Quebec City.
She said some had Alzheimer's disease.
The massive fire in the three-storey building broke out around 12.30am local time, and raged through the night.
Firefighters arrived within eight minutes of getting the alarm and several fire departments in the region were called in to help.
But they were unable to carry out a complete evacuation because of the intensity of the fire. About 20 residents were transported to safety.
Pascal Fillion, who lives near the home, said he ran outside to find a group of locals and firefighters already at the scene, trying everything to save the panicked people inside.
For the most part, he said, rescuers felt helpless against a fast-moving blaze with smoke so thick it was nearly impossible to approach the building.
"People tried to do whatever they could, but the fire was so intense that there wasn't much that could be done," he said.
"I saw people crying, I saw people collapse because they were watching those people burn."
The fire broke out in -20C (-4F) temperatures, causing equipment to freeze, local chief firefighter Yvon Charron said.
The search for the missing was still hampered last night by the cold and thick ice and the fact that the building has collapsed, said Quebec Provincial police Lt Guy Lapointe.
He said late last night that the search for those missing will regroup at daylight.
"We can keep some hope for those unaccounted for, but there's very little doubt that the loss of life is considerable," Mr Harper said.
Retired police officer Pierre Filion, who had a cousin and an aunt living in the residence and who lives nearby, said the tragedy had shaken the tightly knit community of 1,500 people.
"It's going to take a long time to start living normally," said Mr Filion whose missing relatives are both in their 70s.
Parts of the Residence du Havre, which opened in 1997, had sprinklers, while others did not.
At least three people were injured in the blaze. The extent of their injuries was unclear.
The building was home to more than 50 people and also housed a social agency, a pharmacy and a hair salon.
A Quebec health department document updated last July said the building, with one lift, was constructed entirely of wood.
Most residents were older than 75, and 37 of them were older than 85. The building included both single rooms and apartment-style dwellings.
The document indicates the building was only partially fitted with a sprinkler system but did have a fire alarm. There were smoke detectors in every room and in the building itself.
The fire comes just six months after 47 people were killed in Lac-Megantic, Quebec, when a train with 72 oil tankers derailed and exploded in the small community.
In 1969, a nursing home fire in the community of Notre-Dame-du-Lac, Quebec, claimed 54 lives.