MONTREAL -- The roof of a building collapsed on Monday in Blainville, trapping three people beneath rubble, the authorities said.

Firefighters responded to a 911 call around 1 p.m. from a worksite in Blainville, a town in the Laurentians, according to Blainville fire chief Claude Deschuymer.

The roof of a building that was under construction--ostensibly part of a condo complex--had collapsed, Deschuymer said.

Witnesses told firefighters three people were struck in the rubble, so first responders dispatched a specialist in collapsed buildings to the scene.

Firefighters rescued three people--two of whom were transported to the hospital with serious injuries.

An investigation into the cause of the collapse is ongoing, Deschuymer said, adding that the cause of the collapse was unclear.