HELENA, Mont. (AP) — More than 300 firefighters battled three blazes in western Montana on Sunday, and Gov. Steve Bullock declared a state of emergency to allow truck drivers to work longer hours to deliver supplies to the lines.

Bullock said increased demand for aviation fuel and other materials had put a strain on drivers’ hours.

The North Hills Fire north of Helena was threatening roads and structures and prompted evacuations of about 100 homes, but officials said no houses had burned.

The fire had burned 4 square miles by Sunday.

About 140 firefighters, 10 engines and two helicopters were on the scene but had not been able to establish any containment lines, officials said. The fire was believed to be caused by humans.

The Bannack Fire had burned 150 acres (60 hectares) south of Butte. About 70 firefighters — including a state prison crew — built containment lines around 45% of the fire.

Firefighters were pulled off the lines at the Bannack Fire Friday because of the discovery of two 1940s artillery shells that were designed to illuminate battlefields at night. Crews returned Saturday.

The Beeskove Fire northeast of Missoula had burned 115 acres (47 hectares), and officials did not release any containment figures. High winds temporarily grounded aircraft at that fire Saturday. About 125 crew members were on scene.

Both the Bannack and Beeskove fires were caused by lightning.