Story highlights The Canadian city of Fort McMurray is under a mandatory evacuation order

This is the largest wildfire evacuation in Alberta's history

(CNN) Authorities ordered the mandatory evacuation of the entire Canadian city of Fort McMurray in northern Alberta amid a raging wildfire.

Alberta officials issued an expanded order Tuesday. Nearly 53,000 people had moved to safer ground, authorities said.

Extremely high temperatures and low humidity fueled the blaze, leaving firefighters battling "explosive" conditions.

"All our efforts to control and contain the fire were challenged by this extreme fire behavior," said Bernie Schmitte, the forestry manager. "Efforts were also hampered by smoke conditions. Basically fire behavior was beyond all control efforts."

No injuries or casualties have been reported.