Authorities are investigating the death of two Alcoa employees at a smelter in Baie Comeau, Que.
The workers died on Saturday morning in an incident at the company's harbour facilities.
A 30-year-old man was killed after a one-tonne weight fell on him while he was helping load a ship around 10 a.m.
Provincial police said a second worker, 57, suffered a heart attack at the same time, and died later in hospital.
A third man was also injured during the incident.
Transport Canada, Quebec's workplace safety commision and provincial police have launched separate investigations into the deaths.
Alcoa has not commented on the incident.
The company is a global aluminum producer with operations in Quebec and Ontario.
Baie Comeau is about 400 kilometres northeast of Quebec City.