SOME residents warily eyed the driverless "ghost train" as it rushed through the countryside before derailing and crashing into a small Quebec town.

The downtown area of Lac-Megantic was engulfed in flames and now scores of people, perhaps as many as 80, are missing, while around 2000 have been forced from their homes.

Rescuers cautiously entered the charred debris on Sunday, more than 24 hours after the spectacular crash that saw flames shoot into the sky and burn into the night.

Witnesses reported up to six explosions after the train derailed at about 1.20am on Saturday in Lac-Megantic.

Officially, as of late Saturday, only one person was killed and one wounded.

The train, 72 tanker cars loaded with crude oil pulled and pushed by five locomotives, left Montreal, 250km to the west, and was heading to the port of St John on Canada's Atlantic coast.

Instead, its final destination was this picturesque resort town of 6000 residents in a corner of the Appalachian mountains near the border with the US state of Maine.

The town's fire chief, Denis Lauzon, said his department wanted information on what was being moved by rail through his town.

"But we had yet to present a formal request," he said.

Shocked by the force of the accident, residents pressed against police barricades seeking even the smallest detail that could help them cope with the disaster.

Rumours of the runaway "ghost train" quickly spread.

"It had no driver, it was a unmanned train," a young man tells his friends gathered in front of a small grocery store.

Antoinette Paree, 78, remembers seeing "a glimmer, a sort of fire" on the train as it made its way through the night.

Paree arrived home and was looking out from her window, which overlooks the track, when she said she heard "a loud bang - it lit up the whole house," she said.

Paree ran out to save her life, forgetting her dentures and her pyjamas.

The cause of the crash was still unknown but a spokesman for the Montreal Maine & Atlantic company, Christophe Journet, told AFP the train had been stopped in the neighbouring town of Nantes, around 13km 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.

Residents gathered on the far shore of Lake Megantic around a large illuminated cross that dominates the view. There, overnight Saturday into Sunday, they watched much of their town go up in flames.

Linda Rodriguez followed the movement of the flames with her binoculars.

"That's the pharmacy, our home is 50 metres away on the other side of the road," she said.

Another resident, Mariette Savoie, feared the death toll from the "wall of fire" that engulfed her town will be high.

"Above all the Main Street shops were homes," she said.

"All those people who were there were unable to get out."

Originally published as Canada 'Ghost train' toll still unknown