A rail firm and fire department appear to be pointing the finger at one another over a Canada oil train blast that has killed at least 13 people.

Investigators say the tragedy may have been caused by a chain of events stemming from an earlier fire.

Shortly after fire crews put out a blaze on the train, it experienced brake failure, ran away and exploded in the Quebec town of Lac-Megantic.

About 40 people remain missing in the disaster zone.

Some 1,200 of the 2,000 people evacuated from Lac-Megantic are being allowed home on Tuesday.

'Focal point'

The coroner's office has asked families of the missing to provide items such as toothbrushes and combs that might offer DNA samples to help identify the bodies.

Media playback is unsupported on your device Media caption Eyewitnesses say the streets "were filled with fire"

The train, carrying 72 cars of crude oil, was parked shortly before midnight on Friday in the town of Nantes.

An engineer apparently left the train with four of its five locomotives shut down, but kept the final one on to ensure the brakes were engaged.

Officials in Nantes then received a call about a fire on the train.

Transportation Safety Board investigator Donald Ross said: "The extent to which [the fire] played into the sequences of events is a focal point of our investigation."

Nantes Fire Chief Patrick Lambert said that while his crews tackled that blaze, the final locomotive was shut down.

He said this was the standard operating procedure agreed with the train's US owner, Montreal, Maine & Atlantic Railway (MMA).

MMA says the decision to shut off the locomotive to put out the fire could have disabled the brakes.

Shortly afterwards, the driverless train rolled downhill seven miles (11km) before derailing and exploding in Lac-Megantic.

Fire officials said they notified a regional dispatcher for the train company immediately after the initial blaze was put out.

'Hate messages'

Chief Lambert told reporters: "We told them what we did and how we did it. There was no discussion of the brakes at that time.

"We were there for the train fire. As for the inspection of the train after the fact, that was up to them."

Image caption The search goes on for those missing in Lac-Megantic

But MMA's chief executive, Ed Burkhardt, said firefighters should have called an engineer to ensure the train was secure after the blaze.

"If they had actually talked to an engineer he would've known immediately what to do about that," Mr Burkhardt said.

The Chicago-based rail executive is expected this week to visit Lac-Megantic, where he could face a hostile reception.

Media reports quote him as saying he has received a number of hate messages.

At least 30 buildings were destroyed by the fireball that resulted from Saturday morning's explosion, including a store and the public library.

Maude Verrault, a waitress at the Musi-Cafe, a nightspot razed by the blast, was outside smoking when she spotted the runaway train.

"I've never seen a train moving so fast in my life, and I saw flames," she told the Associated Press news agency.

"Then someone screamed, 'the train is going to derail!' And that's when I ran."