Authorities will wait until Wednesday morning to resume the search for two workers presumed buried in the rubble following a landslide at a quarry near l'Épiphanie, Que., 50 kilometres north of Montreal.

Quebec provincial police, working with police and firefighters from the nearby city of Répentigny and from Montreal, as well as provincial civil protection and workplace health and safety officials, soil engineers and other consultants, decided late this evening that conditions were simply too treacherous to risk continuing the search overnight.

"Right now, it's not a safe environment for workers to proceed to the next step, which is to go down to the bottom of the quarry with heavy equipment," said Répentigny police spokesperson Bruno Marier.

Mud, clay 'aggravating factors,' engineer says

Denis Robitaille, an engineer and geologist with Quebec's public security ministry, said getting heavy equipment into place presents a challenge, as there are two to three metres of clay beneath the loose rubble, making the surface extremely unstable.

"In the photos, you can see the viscous mud flowing in places," said Robitaille. "It's a critical aggravating factor [in the rescue effort.]"

Provincial police have now turned over responsibility for the search-and-rescue operation to local authorities, although the force will be providing key support, including helicopters, trained rescue workers and sniffer dog teams, when the search resumes at 7 a.m. Wednesday.

No one inside 1 truck cabin

Following the Tuesday morning landslide, crews using shovels and little else were able to clear away enough rock and clay by mid-afternoon to peer inside the cabin of one of the buried trucks, but found it empty, prompting police to wonder if the driver was ejected from the heavy vehicle when it tumbled as much as 100 metres down the rock face.

One worker was rescued, but two are still missing, following a landslide at a quarry near L'Épiphanie, Que. (Source: Google Maps)

Rescuers have been unable to reach the second truck's cabin.

The quarry belongs to Maskimo Construction Inc., a road construction firm based in Trois-Rivières, Que. with some 20 quarries, sand and gravel pits like the one in l'Épiphanie.

The missing workers are sub-contractors, employed by Allard G. Excavation, Inc. Their identities have not yet been released, except to say they are a man and a woman, both in their 40s. One of them has been operating a truck for the company for 16 years.

"We're all traumatized," said co-worker Sébastien Quévillon. "We can't believe this is happening. It's hell."

A heavy equipment operator watching the slow-going rescue effort earlier in the day surmised the shifting winter weather could have caused the landslide.

"The weather is mild. The ground thaws. It freezes, then thaws again," said Valmont Chaussé, who has worked for Maskimo in the past. "But it could happen in the summer too.... An accident."

One man unhurt

Police and firefighters responded to an emergency call at 10:45 a.m. Tuesday from people who were working at the gravel pit.

Police were able to airlift one person out of the pit by helicopter.

The man, who was driving a loader, was not seriously injured. He was taken to hospital to be treated for shock and effects from exposure to the cold.

Police helicopters lowered search-and-rescue teams to the rocky terrain below. Also taking part in the search were a sniffer dog team and a firefighter with a thermal camera, to scan for heat from the bodies of possible survivors.

"It's kind of a risky, tough situation," Richard said earlier in the day.