The train, which was carrying crude oil, rolled away overnight after it was parked by an engineer. It derailed in the heart of the small town in Quebec's Eastern Townships, forcing close to 2,000 people from their homes.
Witnesses reported between five and six explosions overnight in the town of about 6,000 people. The derailment happened at about 1 a.m. ET, about 250 kilometres east of Montreal. About 1,000 people were evacuated from their homes overnight, and several hundred more also left their homes on Saturday afternoon because of air quality concerns.
Quebec provincial police confirmed one death on Saturday afternoon, and Sgt. Grégory Gomez del Prado told CBC it's possible up to 100 people could be missing, although he said it is difficult to pin down an exact number.
“It’s like the town has been cut by a knife,” he said, referring to the fire that tore through the community's downtown.
Quebec premier Pauline Marois offered her support to the community and Prime Minister Stephen Harper will be visiting the area Sunday to assess the damage and meet with officials.
Harper sent his thoughts out to the community on Saturday afternoon. He said the government was monitoring the situation and was standing ready to provide extra support.
“Our thoughts and prayers go out to the families and friends of those affected by this morning's tragic train derailment," he said in a statement. “We hope evacuees can return to their homes safely and quickly," he said.
Death toll expected to rise
Police said in a news conference late Saturday that they expected the death toll to rise.
"I don't want to get into numbers, what I will say is we do expect we'll have other people who will be found deceased, unfortunately," said Lt. Guy Lapointe, a spokesman with Quebec provincial police.
"We also expect that down the line the number of people who are reported missing with regards to people that who have actually lost their lives will much higher in the sense that there will be more people reported missing that people actually found dead."
Lapointe refused to give any estimate of people unaccounted for because police are having a difficult time getting a number.
"People are calling in reported love ones missing, some people are reported two, three times missing by different members of the family," he said.
Zeph Kee, who lives about 30 minutes outside of Lac-Mégantic, said he saw a huge fireball coming from the city's downtown early Saturday morning.
The area surrounding the explosion site was a popular place on the evenings, and witnesses said the bars and restaurants were bustling with people when the first explosion hit.
Kee said one of the bars, which was packed with people enjoying their drinks on the patio, is now gone along with dozens of other buildings and homes that were flattened by the blast.
Watch the explosion
"It was total mayhem … people not finding their kids," Kee said.
Isabelle Aller, who was visiting the area, says she has been calling her friends ever since the explosion, and they haven't answered their phones.
"The more time that passes, the more we are worried," she said.
Aller says after the first explosion, some people went to the scene to see what was going on.
Several explosions followed afterwards.
Train inexplicably rolls away
The derailed train belongs to Montreal Maine & Atlantic Railway, which owns more than 800 kilometres of track serving Maine, Vermont, Quebec and New Brunswick, according to the company's website.
Chairman Edward Burkhardt said an engineer parked the train west of Lac-Mégantic before he went to a local hotel for the night.
While other details remain unclear, the train rolled away later that night and derailed in the centre of the town.
"He had parked the train, so far as we can determine, properly," Burkhardt said, adding that the brakes were properly applied.
The company will have to wait for clearance from authorities before they can look for more answers.
Burkhardt said that while it's not clear how much oil has been spilled, his company is committed to cleaning up.
"We're pledging a complete cleanup and remediation of the area," he said.
Mayor holds back tears
The teary-eyed mayor of Lac-Mégantic, Colette Roy-Laroche, said emergency services are doing everything possible to deal with the crisis.
"We have deployed all resources to ensure that we can support our citizens," she said.
A spokesperson for Quebec's Environment Ministry says 73 rail cars filled with crude oil were involved. At least four of the cars exploded, sending a huge cloud of thick, black smoke into the air.
The fire, which can be seen for several kilometres, spread to a number of homes. Authorities say some 30 buildings were affected.
"It's dreadful," said Lac-Mégantic resident Claude Bédard. "It's terrible. We've never seen anything like it. The Metro store, Dollarama, everything that was there is gone."
Firefighters called in from U.S.
More than 150 firefighters, some from as far away as Sherbrooke, Que., and the United States, worked from the early Saturday morning to bring the flames under control. While the fire continued to burn in the afternoon, authorities said it had been contained.
A large but as-yet undetermined amount of fuel is also reported to have spilled into the Chaudière River. Some residents say the water has turned an orange colour. Mayor Roy-Laroche assured the public that the town's drinking-water supply is safe, and she encouraged residents to limit their water consumption as much as possible.
Experts from Environment Quebec were also on the scene to keep an eye on the town's air quality.
The cause of the derailment is under investigation.