Police in Lac-Megantic, a lakeside town of about 6,000 people, said they have been unable to determine if there were any casualties. Several people are thought to be missing.
Fire officials said around 30 buildings in the town centre were destroyed, some by the initial blast and others by the subsequent fire. There were reports of up to 60 people missing, although this has not been officially confirmed.
When you see the centre of your town almost destroyed, youll understand that were asking ourselves how we are going to get through this event, a tearful town Mayor Colette Roy-Laroche told a televised news briefing.
The Canadian Broadcasting Corp said four pressurised tanker cars blew up after the train, which had 73 cars in all, came off the rails shortly after 1am. Fire officials said they feared more of the tanker cars were at risk of exploding.
Around 1,000 people were evacuated from their homes.