The wildfire north of Edmonton continued burning Tuesday. (CBC)More than 100 homes were put on evacuation alert Tuesday in counties north of Edmonton because of a wildfire burning out of control and firefighters worried about a shift in wind direction that caught them off guard on Tuesday.

"It's a major worry because … these winds if they're gusting, it's really unpredictable," said Thorhild County Reeve Charles Newell.

A fire covering about 30 square kilometres has been burning in Thorhild County for nearly a week, fuelled by high winds and hot, dry conditions.

A fire sparked by a farmer who hit a rock with his tractor broke out to the northeast of the main fire just after noon on Tuesday, Newell said.

Brydon Ward, a wildlife information officer with Alberta Sustainable Resource Development, said he was concerned about how high winds are affecting crews on the ground.

"That's very tough firefighting weather and the number one concern we have is for the safety of our firefighters," he said. "And that's something we are all worried about."

About 200 provincial and 20 volunteer firefighters are on the scene. Sprinkler systems have been set up outside the houses most at risk.