All four members of a family missing in the wreckage of a house swallowed in a landslide northeast of Montreal have been found dead, officials confirmed Tuesday night.

All four were found in the basement of the Saint-Jude building that was swept away in the landslide on Monday night. Saint-Jude is a town of about 1,000 residents north of St-Hyacinthe near the Yamaska River.

"They were found very close to one another, some of them lying on the couch in the family room in the basement, where we were told that they'd be," said Michel C. Doré, Quebec's associate deputy public security minister, who was on the scene.

'We tried to reach them by phone, because the father always wears his cellphone on him. The firefighters heard the cellphone, but they weren't able to [locate] it.'— Ronald McKinnis, Quebec police sergeant

After searching the ground and first floors of the house, which had shifted from its foundation, officials brought in heavy equipment to take apart the building so they could get to the basement.

The green-roofed home had moved more than 30 metres from its original location, Doré said.

Local authorities said the family's vehicles were parked in front of the house Monday night, leading them to believe that Richard Préfontaine, his wife, Lyne Charbonneau, and their two daughters, Amélie, 12, and Anaïs, 9, were inside when the ground gave way.

Officials had been working on the theory the whole family was in the basement living room watching the Canadiens-Penguins hockey game at the time of the collapse, Doré said.

Members of the family were huge Habs fans, Préfontaine's uncle, Yvon Desrochers told CBC News.

Late Tuesday morning, rescue workers found the family's golden retriever, Foxy, in a pit, caked in mud but in relatively good shape. The dog had apparently been tied up outside at the time of the landslide.

Truck fell into gaping hole

The collapse happened just after 9:30 p.m. on Monday.

The landslide caused a gaping hole more than a kilometre long and a half-kilometre wide. (CBC)

A driver passing through the area by way of the rural road Rang Salvail North alerted police about the massive crater after his truck fell into the hole, said provincial police Sgt. Ronald McKinnis. The driver escaped with minor injuries.

Firefighters briefly approached the collapsed house on Monday night to search for the family, but the ground was too unstable, McKinnis said.

"We tried to reach them by phone, because the father always wears his cellphone on him," McKinnis told CBC. "The firefighters heard the cellphone, but they weren't able to [locate] it."

A police helicopter was brought in and circled the crater for two hours, but no movement was seen, McKinnis added. The helicopter resumed its air search Tuesday morning, aided by police officers on the ground and sniffing dogs.

Landslide shocks tight-knit town

Saint-Jude Mayor Yves de Bellefeuille could find few words to express the community’s sadness after the discovery of the bodies.

"It was a difficult day," he said.

Earlier, de Bellefeuille said he rushed to the crater as soon as police alerted him on Monday night.

The Préfontaines' home fell more than nine metres into the hole. The barn is in the foreground. (CBC)

"It was dark, and we couldn't see well, but we could see the house at the bottom of the crater," de Bellefeuille told CBC's French-language service.

He said he could see the basement was filling up with groundwater.

"It was very hard to look at."

The tight-knit community was in shock, with many admitting to feeling anxious about the risk of more landslides, de Bellefeuille added.

The crater stretches for about half a kilometre and occurred in a region prone to landslides. There was recently another small landslide in the area, Doré said

Five nearby homes were evacuated as a preventive measure. Geological experts arrived Tuesday to determine the stability of nearby homes before giving the go-ahead for families to return.

Doré said it was too soon to say what caused this landslide, but one expert said the fact that southern Quebec sits on an ancient clay seabed makes it prone to this sort of slide.

When fresh water seeps between the clay particles, they liquefy said Michel Bouchard, a geologist with the University of Montreal.

"This is an instantaneous thing. People inside the house didn't have time to react. There is nothing they could have done."

The Prefontaine family home, before the landslide, at 2481 Rang Salvail North in Saint-Jude, Que. (Google Streetview)

A psychologist was sent to a local elementary school, where the younger Préfontaine daughter, Anaïs, is in Grade 4. The therapist will speak with her classmates about the accident, de Bellefeuille said.

Préfontaine works as an electrician in nearby St-Hyacinthe. Desrochers said his nephew's home was built on land that has been in the family for two generations.

Provincial authorities dispatched a trauma team to Saint-Jude's town hall to speak with residents concerned about the safety of their homes, the mayor said.

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