The mayor of Wood Buffalo, Alberta ordered the immediate evacuation of Fort McMurray on Tuesday afternoon, after wild fires rapidly doubled in size and engulfed the city’s main highway.

The massive fires caught the city by surprise, and have left residents scrambling to get out.

Fort McMurray is the home to the Canadian oilsands, which pumps billions of dollars of oil out of the ground — and into the Canadian economy — every year. The fires, if they continue advancing, could threaten much of that infrastructure.

The evacuation order issued by the municipality of Wood Buffalo, which includes Fort McMurray, instructs locals to head north on Highway 63. Fire has already closed a section of that highway to the south, which connects the city to the provincial capital of Edmonton.

The mandatory evacuation order covers a variety of communities in the northern section of Alberta.

Melissa Blake, mayor of the municipality, urged locals to stay calm, but to get out as quickly as possible.

Both Premier Rachel Notley and Prime Minister Justin Trudeau have extended their prayers to those affected, and took to Twitter to encourage those living nearby to obey the evacuation orders.

As of Monday morning, firefighters were optimistic that the fire was contained.

“It’s been a great day for us,” said Fort McMurray Fire Chief Darby Allen, according to Fort McMurray Today. “We’re certainly very happy that no one’s had their properties damaged, no one’s been hurt, and we hope that continues.”

That, however, changed rapidly on Tuesday. Overnight, the forest fires spread rapidly, covering more than 2,500 hectares and wiping out some homes in the area.

By Tuesday afternoon, the fire reached the city’s downtown core.

Dozens of fire fighters are battling the blaze, and eight aircraft have been deployed.