A man who spent the night in a Montreal dumpster is lucky to be alive after he was emptied into a garbage truck and later pulled to safety, one of his rescuers says.

Montreal fire Chief Gilles Ducharme said the man could have been crushed as the truck compressed each load of garbage.

"We had pieces of wood, steel bars, so he was lucky that none of those passed through his body," Ducharme said.

Rescue workers dig for man.

The man is under observation because of the risk of internal bleeding after being compacted in the truck.

Driver Michel Duval was picking up garbage from dumpsters Monday morning when he heard noises from the back of his truck.

He said he had probably dumped a couple of loads on top of the man before realizing he was inside.

Fire and ambulance workers rescued the man, pulling garbage from the truck and leaving a small, smelly mountain of food waste, wood and crushed boxes piled on the ground.

The man was taken to Montreal General Hospital.

James Hughes of the Old Brewery Mission said most homeless people in Montreal sleep in shelters, but some choose to stay outdoors.

"That is often connected with a mental health issue or a very severe social issue," he said.