The worst of the fires, a violent explosion that killed two people at an industrial plant near Sherbrooke, Que., resulted in four people being treated at a Montreal burn unit. The incident, which sent 19 to hospital and destroyed a biotech plant, prompted the city to lower flags to half-mast.
One of the injured, a 42-year-old man, is in critical but stable condition, with burns to 90 per cent of his body. Three other men were seriously burned but were in stable condition. Two of the victims inhaled hot vapour and sustained burns to their respiratory tract.
"The patient with the extensive skin burns also has an extensive inhalation injury," said Isabelle Perreault, who heads the severe-burn unit at the McGill University Hospital Centre.
She noted that the chance of survival from serious burns decreases when a victim also has a significant inhalation injury. Perreault was more confident about the condition of the other patients.
A huge explosion, which could be heard for kilometres, was followed by a series of smaller blasts and a fire, which destroyed a production plant belonging to Neptune Technologies & Bioressources. Amid the wreckage, a terrified survivor was found later, hiding in the rubble.
The company produces health products, such as Omega-3, derived from marine life. Company shares plunged more than 10 per cent and trading was halted after Thursday's explosion.
It's still unclear what caused the fire.
A similar but smaller incident nearby occurred hours later, at a Bombardier Recreational Products complex also in the Eastern Townships.
Two people there sustained serious burns.
Quebec provincial police said the blast occurred just after midnight Friday morning and appeared to come from a lab in the facility's research centre in Valcourt.
It said the victims were a 38-year-old employee and a 54-year-old security guard. Both were taken to a hospital in Quebec City and remained in a medically induced coma early Friday.
The province's workplace health and safety commission was investigating.
The BRP facility produces Ski-Doo snowmobiles, Sea-Doo jet skis and Can-Am all-terrain vehicles. It is located about 40 kilometres west of Sherbrooke, where the massive blast occurred.
Meanwhile, an investigation into a spectacular Montreal blaze was being transferred to the local police. Nobody was injured in that fire, which occurred in an unfinished condo project in Old Montreal.
But the flames lit up the nighttime sky and could be seen jumping above the rooftops in the city's historic quarter, visible even from across the river on the city's south shore.
Police downplayed their role in the investigation. They said their involvement was a routine matter, prompted by the fact that a cause had not yet been determined.
With files from Peter Rakobowchuk