An additional 12,000 people in northwest Alberta have been placed on evacuation alert as an out-of-control wildfire in the area grows.

Mackenzie County issued an eight-hour evacuation alert for a large swath of the county on Saturday afternoon. The alert extends from the outskirts of High Level east to Fort Vermillion, and south towards the mandatory evacuation area around the Paddle Prairie Métis Settlement.

The alert was issued "out of an abundance of caution," due to shifting winds and dry conditions, the county said in a Facebook post.

The alert is intended to give people an opportunity to prepare for a potential evacuation order as the Chuckegg Creek wildfire continues to engulf land southwest of High Level.

The county is asking residents to fuel their vehicles, gather important documents and prepare enough food and water for two to three days.

As of Saturday, the out-of-control wildfire covered roughly 280,000 hectares, nearly half the size of the 2016 Fort McMurray wildfire.

Around 11,000 people have been evacuated as a number of out-of-control wildfires burn across northern Alberta.

There are more than 2,300 firefighters on the ground aided by 228 helicopters, the Alberta government said in an update Saturday.