Huge, fast-moving wildfires have destroyed up to half of the historic Canadian town of Jasper, officials say, as firefighters try to save as many buildings as possible.
Entire streets have been levelled by the blazes in Alberta province, with video showing smouldering rubble where homes once stood.
Cooling temperatures brought some relief on Thursday, but park authorities said the fires were still out of control and further warm weather was forecast.
Meanwhile, there are hundreds of active blazes in neighbouring British Columbia, while fires are burning in western US states including California and Utah.
While no deaths have been reported, some 20,000 tourists and 5,000 residents have fled the mountainous area in Alberta province – a hugely popular tourist spot.
Some 36,000 hectares (89,000 acres) of land has so far been affected, Jasper National Park reported late on Thursday night local time – adding that neighbouring communities were not at risk.
It said that efforts to map the fires had been complicated by factors including strong winds, the extreme nature of the fire, and smoke.
During a news conference on Thursday, a tearful Alberta Premier Danielle Smith struggled at times to recount the scale of the damage, but said “potentially 30 to 50%” of buildings had been destroyed.
“There is no denying that this is the worst nightmare for any community,” she said, adding that Jasper National Park had been “a source of pride” for many generations.
Ms Smith became visibly emotional as she described the beauty of the park and its significance to the community, which relies largely on tourism. Some 2.5 million people visit the park, and nearby Banff National Park, each year.
Rail, phone and power services in the area have been affected, CBC News reported.
Karyn Decore, the owner of the Maligne Lodge in Jasper, was on holiday when she learned her hotel had burned down. On Wednesday night, she received a photograph of the building in flames.
“I was horrified and devastated when I saw that photo,” she told the BBC. “I think it’s going to take a couple of days for the shock to wear down.”
“It’s really hard for everyone to comprehend that we lost one of our properties,” she said, adding that she intended to rebuild the lodge.
BBC journalist Wendy Hurrell was in Jasper National Park when the fires began to burn on Monday. She drove through the night with her husband and daughter in a rush to leave town.
“The storm was ferocious – the skies went dark red and there were whipping winds, fierce rain and lightning,” she said.
“We are some of the last travellers to see Jasper in its full beauty – it will be a very long time before it will recover. It’s utterly devastating for them all and my heart is breaking.”
Hundreds of firefighters from around the world have been deployed to help with the response, but officials warn the extent of the damage is still emerging. The focus on Thursday, they said, was on containing the towering flames which engulfed the town from two sides.
Pierre Martel, director for the national fire management programme at Parks Canada, said the fire was started by a lightning storm and escalated late on Wednesday as it was fanned by powerful winds.
“It [was] just a monster at that point,” Mr Martel said. “There are no tools we have in our tool box to deal with it.”
The flames reached 100m (328ft) high in some places, covering “an inordinate amount of space in a very little amount of time”, one official said.
Mike Ellis, Alberta’s minister for public safety, said the fire was 5km (3 miles) outside of Jasper when it was pushed by the winds to the town in “less than 30 minutes”.
“Any firefighter will tell you there is little to nothing you can do when you have a wall of flames coming at you like that,” he said.
“Nobody anticipated that fire to come so fast, so large and so quickly.”
Justin Trudeau, Canada’s prime minister, thanked the emergency services for their response to the wildfires.
“As the heartbreaking images from Jasper emerge, I want to thank the brave first responders who are in Alberta right now, fighting to save every home and every community they can,” he said.
This marks another year of difficult fire conditions for the province. Last year, a record 2.2 million hectares burned in Alberta between 1 March and 31 October.
Other parts of western Canada and the US hit by fires
In British Columbia, the province neighbouring Alberta to the west, more than 400 wildfires have been burning and dozens of evacuation orders have been issued.
In the US, more than 3,000 people have been forced to flee their homes in the state of California due to the Park Fire, which continues to rage out of control.
A man has been arrested in connection with the blaze, the California Department of Forestry and Fire Protection, also known as Cal Fire, said.
The states of Oregon, Montana and Utah also continue to deal with wildfires.
The overall number of fires has decreased around the world over the last two decades.
But researchers say climate change could bring more lightning to forests in northern reaches of the globe, increasing the risk of wildfires.
With additional reporting from Eloise Alanna and Ottilie Mitchell