The collapse of a warehouse roof in Morin Heights, Que., in which three women were killed follows the recent cave-ins of about two dozen other building roofs, blamed on the region's heavy snowfall.

Provincial police said they suspect the snow-laden roof caused the Gourmet du Village warehouse to collapse and catch fire on Wednesday. But police are still investigating the cause, including whether any structural problems led to the accident.

Four hours after the cave-in, emergency workers pulled out the bodies of three women. The victims, who were 46, 54 and 62, all worked at the grocery warehouse.

Some of the roughly 45 employees who had been inside said they heard cracking sounds and shifting snow before the roof fell.

The Quebec workplace safety commission is also investigating the incident. It encouraged employees across the province Thursday to report worrisome workplace conditions.

"If an employee feels at risk, they have the right to refuse to work," in which case the commission can intervene, spokeswoman Alexandra Reny said.

Meanwhile, the mayor of Morin Heights, a town of 2,700 located in the Laurentians, has closed the local elementary school until the school board clears its roof.

Aimé Charette, spokesman with the Montreal fire department, said at least 20 roofs have collapsed under the weight of the snow in the last few days. The department has also received 100 calls about roofs threatening to collapse since the weekend.

Charette said people should clear the snow off a roof before it becomes a problem.

"When there's a heavy snowfall on a flat roof it's dead weight," Charette said. "It depends what other equipment you have on the roof — air conditioning and so on — this also adds to the load. So it really depends on the structure."

He said the owner should consult an architect or an expert in the field as soon as snow starts accumulating.