The death toll from the Lac-Megantic train disaster rose to 28 on Friday after four more bodies were pulled from rubble of the devastated Canadian town.
A further 22 people remain missing and presumed dead after the rail disaster, Quebec police said, as accident investigators continue to comb through the destruction.
A spokesman from the coroner's office added they have now identified eight of the 28 bodies, up from just one earlier.
Part of a train made up of 72 tank cars loaded with crude oil derailed in the early hours of Saturday in Lac-Megantic, near the Quebec-Maine border, igniting a huge explosion that laid waste to the center of the lakeside town.
Police working in the disaster zone have had "a great deal of difficulty" because of strong petrol fumes, Quebec provincial police spokesman Michel Forget said.
"These are the places where there is a much denser concentration of oil. So, when we lift pieces, these fumes" reach insupportable limits for the investigators, he explained.
"We have had therefore to review our strategy and deploy to other spots," Forget explained, emphasizing that "the ground is contaminated with oil in some places."
Police are examining "different measures to ensure ventilation to make sure the work can continue" as efficiently as possible.
The approximately 200 police on the scene, including 60 investigators, will be reinforced in the coming days by crime scene technicians from Montreal and Quebec City "in order to accelerate the work," he added.
Earlier, investigation official Jean Laporte said the Lac-Megantic crash was "extremely likely the most devastating rail accident in the history of Canada."
The US transportation safety agency will also come help the investigators, Laporte added.