L'EPIPHANIE, Que. -- An inability to clearly see the precariously shifting ground beneath them caused rescue crews to suspend their search Tuesday night for two Quebec quarry workers who are missing after an apparent landslide swept several vehicles into a pit nearly 100 metres deep.

Two trucks and an excavator were trapped in huge mounds of loose gravel at the bottom of the snowy crater in L'Epiphanie, Que., just east of Montreal.

A third worker had managed to climb out of the excavator with what police described as minor injuries, after the vehicle tumbled down the steep embankment.

"Since we are not able to see what is going on and to confirm the security of the people that's involved in the search and rescue, right now it's going to start again tomorrow morning," provincial police spokesman Benoit Richard said Tuesday night, adding that specialists at the rescue site had recommended the suspension.

Rescue workers will attempt to bring heavy equipment down to the site on Wednesday morning, and will continue to use search dogs and thermal equipment in their attempts to locate the missing workers.

"Tomorrow we're going to try a safe protocol or procedure for everyone to be safe and try to bring the excavator and other heavy equipment down on the ground. That's our main concern for tomorrow," said Repentigny, Que., police spokesman Bruno Marier.

Helicopters had been making numerous trips into the narrow crevasse of the quarry earlier on Tuesday, where the vehicles were strewn about like toys.

A chopper had to be used to airlift the worker who clambered out of the quarry. Richard said the man suffered from frostbite, shock and minor injuries.

"He seems, overall, in pretty good shape," he said.

Two helicopters swooped into the pit numerous times during the day to drop off police officers, firefighters, geologists and a sniffer dog.

Armed with shovels and a thermal camera, rescue teams sifted through the heavy gravel in hope of finding the missing workers.

Rescuers managed to remove enough stone to peer into the cab of one of the trucks -- but police said nobody was inside. The vehicle was partially buried in the gravel and was lying almost completely upside down.

By nightfall, neither of the workers had been found.

"We haven't found anybody," Richard said. "We need to find them."

Richard had initially told reporters the search would continue into the night, and that the helicopters could operate in the dark, however the unstable soil in the pit combined with working in the dark resulted in the search being suspended.

"Time is working against us," Richard had said, adding that rescuers still had no ground access to the bottom of the steep quarry.

Reporters asked an official from the Public Security Department about the survival chances of the workers.

"I'm not a doctor, but for sure time is passing and it's not a good thing," Paul Lefebvre told a media scrum.

The local mayor watched rescue operations anxiously from the lip of the quarry.

"Anything is possible, but we're crossing our fingers and we're waiting," Denis Levesque said as police choppers rumbled above his head.

"We're in shock right now and it's a lot of things to manage in a short amount of time."

An employee at the quarry, which is operated by Maskimo Construction Inc., told Radio-Canada that workers were "traumatized" by the incident.

"We can't believe that this happened -- it's hell," Sebastien Quevillon told the French-language TV network.

Before the earth apparently gave way at the top of the quarry, the excavator was filling the trucks with gravel at the site.

Authorities were investigating the cause of the apparent landslide.

Late Tuesday, a geologist advising search crews said the excavation of the site, combined with the nature of the pit's underlying clay soil sandwiched between gravel which had been excavated, may have led to the slide.

"Right now it's an hypothesis," said Richard. "We are at the start of the investigation, we're going to work with our partners to find what caused the landslide."