At least 80 people are missing and three confirmed dead after a driverless oil tanker train derailed and exploded in the small Canadian town of Lac-Megantic, destroying dozens of buildings.

The accident in the small Quebec town, located around 250 kilometers (155 miles) east of Montreal, created a large fireball and forced 2,000 people from their homes.

Officials confirmed at least three deaths on Sunday after a search for bodies.

A firefighter returning from the scene told AFP on condition of anonymity that there had been at least 50 people in one bar that was consumed by the flames.

"There is nothing left," he said.

Witnesses reported as many as six explosions after the train derailed at about 1:20 am in Lac-Megantic, a picturesque resort town of 6,000 residents near the border with the US state of Maine.

Michel Brunet, a spokesman for Quebec's provincial police, said late Saturday the official death toll remained at one, but added: "We expect there will be more fatalities."

Radio-Canada had earlier reported that 60 people were unaccounted for in Lac-Megantic, where the blaze was still raging, 20 hours on.

Brunet said there have been "several reports" from people who said they were unable to reach relatives who lived near the accident site.

"The fire is still raging, our investigators have not yet even been able to get close to the scene," he said, more than 12 hours after the incident.

An initial evacuation zone of a kilometer around the crash site was widened Saturday as a precaution against harmful particles in the air, bringing the number of people forced to leave their homes to a total of 2,000.

Around 150 firefighters were battling the blaze, including some who came across the border from Maine, just 25 kilometers south of the town.

'No conductor on board'

The cause of the crash was still unknown, but Christophe Journet, a spokesman for the Montreal Maine & Atlantic company, told AFP the train had been stopped in the neighboring town of Nantes, around 13 kilometers west of Lac-Megantic, for a crew changeover.

For an unknown reason, Journet said, the train "started to advance, to move down the slope leading to Lac-Megantic", even though the brakes were engaged.

As a result, there was no conductor on board when the train crashed, he said.

A team of investigators from Canada's transportation safety agency was quickly dispatched to the scene to investigate.

One witness, Nancy Cameron, posted a photo on social media websites showing one of the train's locomotives spouting flames near Nantes.

Other witnesses were in Lac-Megantic when the train came barreling in.

"When we came out of a bar, we saw cars arriving in the center of town at full speed," Yvon Rosa told Radio-Canada.

"We heard explosions and there was fire everywhere. We ran to the edge of the water," Rosa said.

Prime Minister Stephen Harper offered his "thoughts and prayers" to the community and said the federal government was ready to provide assistance.