HOYT LAKES (AP) - Crews working by air to fight wildfires in northern Minnesota are being interrupted by intrusions into restricted airspace.

The Minnesota Incident Command System says aerial firefighting operations were temporarily ceased in recent days because a private plane intruded into the airspace and a second time because an unmanned aircraft system, or drone, entered the firefighting zone.

Fire officials say when an unauthorized plane or a drone is spotted over fires, aerial firefighting operations must stop immediately. When aircraft are needed to fight a fire, a temporary flight restriction is enacted for the airspace above and around the fire. Those who fly into that zone are subject to various penalties, fines or loss of license.

Crews battling a wildfire that has burned 1,000 acres east of Hoyt Lakes have the blaze 57 percent contained.