HELENA, Mont. — A lightning-caused wildfire in western Montana prompted evacuations just outside the capital city of Helena on Thursday, and some residents on the south side of the community were told to be ready to leave if necessary.

Authorities could not say how many people were told to evacuate, but no homes had burned and no injuries were reported, fire information officer Kathy Bushnell said.

The fire started Thursday, and winds soon pushed it across 300 acres (1 square kilometer), Bushnell said.

The fire was about 2 miles south of Helena, she said.

Four large air tankers and four helicopters were on scene, including one National Guard chopper.

Winds were blowing toward the east Thursday and would have to shift toward the north to threaten Helena, said Paul Spangler, disaster coordinator for Jefferson County, which includes the city.

Helena, with a population of about 31,000, is Montana’s sixth-largest city.

The evacuation order covered residents in a forested area west of Interstate 15 between Helena and Montana City, about 5 miles to the south.

Evacuation orders were still in place around Florence, about 125 miles west of Helena, where the Lolo Peak Fire has burned 53 square miles (138 square kilometers) since it started in mid-July.

Ravalli County emergency management officials said about 150 homes south of Florence were evacuated Wednesday night because erratic winds created dangerous fire behavior.

The Lolo Peak Fire was also caused by lightning.

Most of Montana is in a drought, and the northeast corner has been particularly hard-hit.