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Rescue crews were carefully combing through the icy rubble of a seniors' home that burned to the ground Thursday morning in a fire that killed at least five people and injured 10 others, authorities said.

About 30 people remained unaccounted for in temperatures near zero Thursday night, and the death toll was expected to rise, Quebec police said. But rescuers were still holding out hope that some of those missing might have been away with their families when the enormous fire ravaged the 52-unit Residence du Havre in the small community of L'Isle-Verte shortly after midnight.

Eight of the 10 people who were injured were being treated at a local hospital for burns, falls, smoke inhalation or carbon monoxide poisoning, health officials said, while the two others were flown to a trauma center for emergency treatment.

Quebec Provincial Police Lt. Guy LaPointe said crews were using Thursday night to get their equipment in place so they could resume the search for victims as soon as daylight broke Friday. The work is likely to be long and hard — both because of the sub-zero weather and because it was important to find everyone who might be buried in the ashes.

"With the weather, just to push the flames, we needed to use water, and it froze," LaPointe said. "Our priority is to work not only in a secure fashion but to preserve the integrity of the victims."

LaPointe said there was no timetable to for how long the search might take. The amalgam of ice, ash and still-smoldering embers made for a dangerous and "very nasty scene," he said.

The fire, which authorities said began about 12:30 a.m. ET, destroyed the three-story wooden complex, lighting up the night sky like a bonfire.

Alphonse Gagnon, 79, and his wife, Yvette Michaud, 73, watched it burn from their home across the street. They didn't see anyone escape, they told NBC News.

"The fire was so red [that] it lit up everything. ... I saw all of the tragedy," Michaud said in French. "We spent the whole night watching."

Michaud said authorities set up a white tent at the site, possibly for the dead. She said a number of the residents, most of them older than 75, used wheelchairs or suffered from illnesses, such as Alzheimer's.

"It was frightening," said Michaud, adding that she was shaking as she watched the blaze, thinking about her friends inside. "It's so dreadful."

Collette St. Laurent, 77, who lives near the home, said she knew people who lived in the three-story complex.

"It's a village. Everyone knows each other. It's heartbreaking, so heartbreaking," she said.

She hadn't gone by the site but feared for the missing: "They must be in the ashes. ... They couldn't save them," she said.

Witnesses described the chaotic blaze as "spreading fast as gunpowder."

Mario Michaud, a longtime resident who lives across from the complex, told NBC News that he awoke just after midnight to go to the bathroom when he saw the fire from one of his windows.

"It burned. It burned. ... It was so engulfed in fire," Michaud, 78, said in French. "Everything is burned."

Michaud said he saw people trapped in the home, some of whom he said jumped from their balconies.

A man fetched a ladder to try to reach his mother, who was stranded on a balcony, "but he wasn't able to get her down," Michaud said.

Aerial view of senior complex in Quebec after a fire on Jan. 23, 2014.Quebec Provincial Police

The fire's fury raised questions about whether the complex, built in 1997, had functioning sprinklers. According to Residence du Havre's website, the building has a fire alarm zone, sprinklers and smoke detectors in every room.

A residence certification on file with Quebec's Health Ministry says the home has a partial system. It also says the building was constructed entirely of wood.

Yves Desjardins, who helped build the residence, told CBC News that only a newer annex to the complex built in 2002 had a sprinkler system.

"There were probably some small things that had to be corrected everywhere," the official, René Dumont, told the Gazette — problems like missing signs showing emergency evacuation routes.

The agency fully certified the residence shortly thereafter after it corrected the problems, Dumont said, adding that fire officials noted that "there was a lot of training and practice that was done, with excellent cooperation from the residence."

"It's a village. Everyone knows each other. It's heartbreaking, so heartbreaking." — Collette St. Laurent

Quebec's minister for labor and social solidarity, Agnes Maltais, said at a separate news conference that the government would review whether all older homes for senior citizens should have full sprinkler systems.

"In fact, we believe they are well-protected, but we always have to tighten the rules each time we see there's a failure somewhere," Maltais said.

"If the investigation shows anything missing, you can be sure that we will act accordingly," she said.

Pierre-André Fournier, the Catholic archbishop of Rimouski, said the fire would have ramifications far beyond the small town on the St. Lawrence Seaway about 150 miles northeast of Quebec City.

Those who died probably had many children, grandchildren and great-grandchildren, he said, meaning "it's all of Quebec that is affected by this tragedy."

The fire comes six months after another deadly blaze in Quebec killed 47 people. An unattended freight train carrying oil derailed, creating a powerful explosion that destroyed the downtown of Lac-Megantic, a community on the Maine-Quebec border.

Alexandra Moe and Erik Ortiz of NBC News contributed to this report.