Dangerous conditions are hampering the search for 40 people missing after a runaway crude oil train blew up in a Quebec town, killing five.
Fire crews were unable to search Lac-Megantic overnight because dozens of tanker wagons are strewn across the site after the blast early on Saturday.
Canadian Prime Minister Stephen Harper said the place looked like "a warzone" as he toured the area on Sunday.
At least 30 buildings were incinerated by the fireball.
"It's an area that is still extremely risky," police spokesman Benoit Richard said on Monday. "The fire service decided they could not allow us to go there for security reasons. We'll see what we can do today."
Many of those missing were believed to have been drinking at a popular downtown bar when the explosions occurred, he added.
Anne-Julie Huot, 27, said at least 25 people she knows are still missing.
"I have a friend who was smoking outside the bar when it happened, and she barely got away, so we can guess what happened to the people inside," she told the Associated Press news agency. "It's like a nightmare."
One man who escaped from the bar told CBC that he had not been able to sleep because he keeps hearing the screams of his friends.
None of the dead have been identified, and the five bodies recovered so far, all badly burned, were being sent on Monday to Montreal for identification.
Officials have warned that some of the dead may never be recovered, given the intensity of the fire.
Police are encouraging family members of the missing to contact officials to help with the search.
Among buildings in the town destroyed were a grocery store and the town library.
Firefighters worked over the weekend to put out remaining fires.
On Monday, they were dousing two oil-filled cars with water and foam in an attempt to keep them from overheating and exploding.
Crews are also working to contain 100,000 litres (27,000 gallons) of crude oil that have spilled into nearby waterways.
A spokesman for Quebec's environmental ministry says floating barriers and other methods are being used to block the oil from heading downstream.
But the pollution has already reached the nearby town of Saint-Georges, prompting fears oil could flow into the St Lawrence River.
The train had been parked in the village of Nantes, about 7km (four miles) from Lac-Megantic, during an overnight driver shift-change on Friday evening.
Firefighters from Nantes were later called to put out a small fire on the train, but it is not clear if that was linked to what happened next.
Sometime afterward, 73 cars carrying pressurised containers of crude oil became uncoupled from five locomotive engines, gathering speed as they rolled downhill before derailing in the heart of Lac-Megantic, which is about 250km east of Montreal.
An official statement from the train operator said the brakes on the locomotive had somehow completely shutdown after the engineer left the train.
This "may have resulted in the release of air brakes on the locomotive that was holding the train in place", the firm said.
The explosion sent a fireball and black smoke into the air, forcing the evacuation of 2,000 people. Of those, 1,500 are unlikely to return to their homes immediately, officials said.
Prime Minister Harper said an "unbelievable disaster" had befallen Lac-Megantic, as he toured the town on Sunday.
Canada's transportation safety board has retrieved the train's data recorder and a separate device that contains details of the braking system.
The train had been travelling from the Bakken Field in North Dakota to a refinery in Saint John, New Brunswick.