ROUNDUP, Mont. (AP) — Officials say 10 to 15 structures have been destroyed in south-central Montana and evacuations have been ordered ahead of a fast-moving wildfire that grew to at least 23 square miles on Saturday since starting a day earlier.

Fire spokesman Paula Short says the destroyed buildings are believed to be secondary structures and no injuries have been reported.

She says the Delphia Fire is in a rural area about 14 miles northeast of Roundup burning in grass, sage and timber. Musselshell County officials have ordered residents along Fishel Creek Road to evacuate, and residents along Hawk Creek Road are under a pre-evacuation notice.

Short says about 30 to 40 homes are threatened.

She says more than 100 firefighters are battling the fire along with four air tankers and three helicopters.