The Fort McMurray fire is growing further and could spill in to neighboring province of Saskatchewan, Canadian officials say.
Hot, dry and windy conditions are hampering efforts by hundreds of firefighters to tackle the blaze.
The blaze has already caused the evacuation of 80,000 people from the oil city of Fort McMurray, and thousands are still stuck to the north.
Their evacuation, originally planned for May 7, will now take place on May 8.
Alberta Premier Rachel Notley said: “In no way is this fire under control.”
The wildfire now covers an area of more than 700 sq miles, which includes areas still ablaze and areas already burnt.
It was being propelled by high winds to the north-east towards Saskatchewan.
Smoke from the fire has already spread there, and air quality statements have been issued for both Saskatchewan and North-West Territory.
“Fire conditions remain extreme,” said the Alberta Emergency Management Agency on May 7.
There is the possibility of rain on the next days, but officials say the fire can only be put out by sustained heavy rains.
Earlier this week, most evacuees headed south but some fled north, sheltering in work camps beyond Fort McMurray.
Thousands have since been shuttled out by road and air, with small convoys passing through the fire-ravaged city on May 7.
The blaze has ruined entire neighborhoods, with residents warned it could be some time before they can return. Officials say the power grid is damaged and the water not drinkable.
As much as a quarter of the country’s oil production has been halted by the fire, raising concerns about the effect on the Canadian economy.