Park County officials have ordered a mandatory evacuation for an unknown number of residences due to a grass fire burning about 15 miles south of Livingston.

NBC Montana has a reporter at the scene.

The fire started at about 1 p.m. Wednesday west of U.S. Highway 89 south and had traveled nearly 4 miles. Temperatures in the area were in the low 90s Wednesday afternoon.

County officials say the evacuation was ordered for residences west of Inverness Road, but officials did not know how many houses were affected.

The Livingston Enterprise reports a sheriff's deputy was hosing down a propane tank at one house. About 30 people were working on the fire.

The cause and amount of area burned by the fire are unknown.

NBC Montana will keep you updated with the latest details as we learn more.