Quebec provincial police Lt. Michel Brunet said Sunday that about 40 people have been reported missing, but cautioned that the number could fluctuate up or down.
Brunet confirmed two more deaths early Sunday afternoon after confirming two people were found dead overnight. One death was confirmed Saturday.
More than 1,000 people were evacuated when several tanker cars of the Montreal Maine & Atlantic train exploded in the downtown area and fire spread to a number of homes. Rescuers had a difficult time reaching part of the 73-car train due to the blaze. Flames and billowing smoke could be seen hours after the train derailed around 1 a.m. Saturday.
The search for victims in the charred debris was hampered because several tanker cars were still burning Sunday morning, sparking fears of more potentially fatal blasts.
Lac-Megantic, which is located about 155 miles east of Montreal, is home to about 6,000 people.
According to the railway's operator, the cause of the accident was believed to be a runaway train. The president and CEO of Rail World Inc., the parent company of Montreal, Maine & Atlantic Railway, said the train had been parked uphill of Lac-Megantic because the engineer had finished his run. The tanker cars then sped downhill into the town before derailing.
The Associated Press contributed to this report.