High winds and hot temperatures may worsen a huge wildfire that has forced the entire population of a Canadian city to be evacuated, officials say.
Some 80,000 people in Fort McMurray, in Alberta province, fled the flames but no injuries have been reported.
Fires in the city's buildings were extinguished overnight but some districts were badly hit and the situation may deteriorate at any time.
Large areas of Alberta and Saskatchewan are under extreme fire risk.
Help from the army and air force is being sent to Fort McMurray but may take two days.
The mandatory evacuation order for Fort McMurray is still in effect and the 10.25 sq mile (2,656 hectare) fire there is still listed as out of control.
The blaze broke out south-west of the city on Sunday. Firefighters appeared to have a measure of control by Tuesday until a drastic wind shift overwhelmed them.
The chief of Fort McMurray's fire department, Darby Allen, said on Wednesday: "Firefighting staff have worked throughout the night, and all fires within the city have been extinguished.
"There are still some hot spots in the wild land, and that mixed with the wild land fire outside the city is what we are worried about for the rest of the day.
"It could be even more devastating unfortunately."
He said: "It's a nasty, ugly fire and it's not showing any forgiveness. The community is going to be devastated. This is going to go on. This is going to take us a while to come back from."
Alberta agriculture and forestry manager Bernie Schmitte said: "The worst of the fire is not over. We're still faced with very high temperatures, low relative humidity and some strong winds."
Brian Jean, leader of Alberta's opposition, said on Tuesday night: "My home of the last 10 years and the home I had for 15 years before that are both destroyed."
The Beacon Hill suburb was said to have lost 80% of its homes. A CTV reporter there said there was almost nothing left. "It's just blocks and blocks of soot, basically," she said.
Serious losses were also reported in Abasand and Waterway. One street in Timberlea lost a dozen trailer homes.
Some 150 firefighters are tackling the blaze, backed up by nine air tankers and more than a dozen helicopters, officials say.
'Roofs coming down'
Tens of thousands of people took to the roads that were still passable to flee the city, creating long lines of vehicles. Mr Schmitte said there was no fuel left in Fort McMurray.
Communities were throwing open their doors to help the evacuees, although many headed towards Edmonton, Alberta's capital, some 270 miles (430km) away.
Alberta Premier Rachel Notley called it the "biggest evacuation... in the history of the province".
A terrifying experience: Szymon Bicz, eyewitness
"I'm on the road to Edmonton, after managing to escape Fort McMurray in a hurry. It's chaos here. Everyone has been advised to evacuate immediately. The roads are gridlocked.
The smoke was really overpowering. It was a terrifying experience. I was at work listening to the radio for updates, where they were saying it was contained initially.
Then it spread really rapidly. I drove back to my house and grabbed my passport and some clothes and started driving out of town with a colleague. My family have not moved over yet from the UK.
The thick black smoke was closing in and surrounded the car. People were driving up on paths and grass verges just to get out of there. I'm hoping my rented house is still intact but I just don't know.
The whole region is at risk. It's absolutely catastrophic, but people here are big-hearted. Volunteers on the highway to Edmonton are giving food and water as required."
One fleeing city resident, Cassie White, told the Globe and Mail flames had crossed a road and blown up a petrol station.
She told the paper: "There were flames maybe 15ft high right off the highway. There was a dump truck on fire - I had to swerve around it - and there was a pickup truck on fire as well. The entire trailer park on my right was in flames. Roofs were coming down."
PM Justin Trudeau said on Wednesday he had offered Alberta his support.
He said: "We all have to work together to come to the aid and support of people who are experiencing terrible tragedies, losing their homes, their jobs and everything they own."
Fort McMurray is a major centre of Canada's oil sands industry - with vast oil reserves - and a major evacuation of staff was ordered.
Suncor Energy said its main plant was so far safe but crude production was being cut.
Shell Canada said it was opening its camp to evacuees.
Canada Post has suspended all deliveries to Fort McMurray.
Fort McMurray: Canada's 'manliest' city
On its tourism website, Fort McMurray describes itself as the "gateway to the north" - a region which is home to the third largest reserves of oil in the world behind Saudi Arabia and Venezuela.
It may be remote, but Fort McMurray's proximity to Canada's rich oil sands has helped it to become a hugely prosperous place, drawing oil workers from across the world.
It is not strictly speaking a city, but such has become Fort McMurray's importance in the region that it is commonly referred to as one.
Canada's National Post called Fort McMurray 'Canada's manliest city' where men outnumber women by roughly three to two.