The entire population of Fort McMurray, Canada, has been ordered to evacuate as a wildfire whipped by winds engulfed homes and sent ash raining down on people.
More than 80,000 residents of the Alberta oil sands city were ordered to flee after an earlier order that had applied to nearly 30,000 people, mostly on the south side, was extended to tens of thousands more as flames continued to make their way into the city.
Panicked residents packed Highway 63, the only route out of the city, as flames jumped across the road.
The wildfire, whipped by unpredictable winds on a day of high temperatures, worsened dramatically in a short time and many had little notice to flee.
Alberta premier Rachel Notley said officials were doing all they could to ensure everyone's safety and were looking into a possible airlift for residents with health issues.
Brian Jean, the leader of Alberta's opposition party who lives in the city, said much of central Fort McMurray was being destroyed by the fire. He said flames were encroaching on the city centre and the city's evacuated hospital was on fire.
"Our hospital is on fire, where my children were born," he said. "My home of the last 10 years and the home I had for 15 years before that are both destroyed."
Scott Long of Alberta Emergency Management said the flames burned a number of structures.
Carol Christian's home was in one of the neighbourhoods under the order to leave. She said it was scary as she drove to an evacuation centre with her son and cat.
"When you leave it's an overwhelming feeling to think that you'll never see your house again," she said.
"It was absolutely horrifying when we were sitting there in traffic. You look up and then you watch all the trees candle-topping up the hills where you live and you're thinking, 'Oh my God. We got out just in time'."
The main road into Fort McMurray was closed at the southern entrance to the city after flames jumped the road. Pictures posted on Twitter showed long lines of traffic and skies darkened by thick smoke as flames licked the edges of roads.
Fort McMurray is the capital of Alberta's oil sands region. The Alberta oil sands are the third largest reserves of oil in the world behind Saudi Arabia and Venezuela.
Canadian prime minister Justin Trudeau tweeted that he spoke with Ms Notley and the government stood ready to help. He urged residents to follow evacuation orders.
Oil sands work camps were being pressed into service to house evacuees as the raging wildfire emptied the city. Most oil sands projects are well north of the community, while the worst of the flames were on the city's south side.
Officials were also evacuating non-essential staff at Suncor's base plant, 18 miles away and one of the closest facilities to the city. Spokesman Paul Newmarch said evacuees were moving into the plant's work camps.
Will Gibson, a spokesman for Syncrude, which also has a plant north of the town, was himself one of the evacuees heading north away from the flames.
He said he had to flee his neighbourhood via a grass embankment because the fire had already cut off the road at both ends.
"I left my neighbourhood and there were houses on fire," he said. "I don't know if and when I'll be going back."
The large work camps can normally accommodate thousands.
A local radio reporter said a trailer park that had been evacuated on Monday was on fire and flames were advancing towards businesses.
"It's chaos on the roads. People are panicking. It's gridlock on the roads. Flames are right next to a gas station," said Carina Van Heerde of KAOS.
Crews had seemed to be making progress controlling the blaze, burning since the weekend, but the situation worsened quickly on Tuesday. By mid-afternoon people from three neighbourhoods were told to leave immediately.
Unseasonably hot temperatures combined with dry conditions have transformed the boreal forest in much of Alberta into a tinder box. The wildfire threat ranged from very high to extreme in different areas.
The Alberta government banned all open fires except in designated camping sites in forested areas due to the threat. There were about 30 fires burning in the province.
The province was calling in more reinforcements to Fort McMurray, including 100 more firefighters and a giant helicopter that can dump more than 500 gallons of water at a time.
Fire chief Darby Allen said the service did not have an estimate of the number of homes destroyed, but the fire was burning in several areas in the city's south end and had destroyed a mobile home site.
There had been no reports of serious injuries and Mr Allen said the immediate priority was to keep everyone safe.
Crews are trying to maintain the crucial infrastructure in the city, including the only bridge across the Athabasca River and Highway 63.