The crews are up against extreme cold and a thick coating of ice over the rubble, say police.
Around 20 people were rescued and brought to nearby health centres and hospitals shortly after the fire started around 12:30 a.m. ET Thursday.
A total of 52 people were listed as living in the building, but Quebec provincial police are still trying to pin down how many of them were inside at the time of the fire.
Police are expected to provide another update at the scene at 9 a.m. ET.