A state of emergency has been declared in the province of Alberta in Canada after a wildfire forced all 88,000 residents of Fort McMurray to flee.
Officials warn that the fast-moving blaze could destroy much of the city and the next 24 hours will be crucial.
The fire, which broke out on Sunday, has gutted 1,600 structures, including a new school, in Fort McMurray.
The evacuation was the largest in Alberta’s history. Nearby oil companies have been forced to cut output.
Several firms operating in Alberta’s oil sands region have shut down some pipelines.
This was done to help evacuate non-essential personnel, reports say.
So far there have been no reports of injuries in the wildfire.
Bernie Schmitte, an official at Alberta’s Agriculture and Forestry Ministry, said on Wednesday that the “catastrophic fire” had so far “resisted all suppression methods”.
After flying over the burning city, Alberta Premier Rachel Notley said the blaze had moved north and east across Fort McMurray.
If the winds behaved as predicted, she added, the blaze would move into the Thickwood and Timberlea communities, as well as the area around the airport.
“Bad news does not get better with time,” said Scott Long, executive director of Alberta’s Emergency Management Agency.
“It is a possibility that we may lose a large portion of the town,” he added.
Officials said the size of the blaze was now more than 10,000 hectares (39 sq miles) and it was being tackled by 100 firefighters.
Fire services said high winds and hot temperatures were helping the blaze to spread over an even greater area.
Ms Notley praised Albertans for helping neighbours in need.
“We will get through this and we will come out stronger on the other side,” she said.
Unseasonably high temperatures and strong winds have combined with dry conditions to leave much of Alberta and neighbouring Saskatchewan under an extreme fire risk warning.
Prime Minister Justin Trudeau said he would send military aircraft to help if they were needed.
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.