Two fast-moving wildfires - including a new one that tripled in size overnight - have triggered new evacuations in southeastern Montana.

Firefighters are battling a potent mix of lightning strikes, dry weather and flame-whipping winds as they try to contain the 290-square-mile Ash Creek fire near Ashland and the 9-square mile Horse Creek fire south of Hysham.

Authorities say the Ash Creek fire jumped Highway 212 west of Broadus early Monday. The Powder River County Sheriff's Office was evacuating Sonnette and Ten Mile Creek roads.

The Horse Creek fire is the largest of more than a dozen fires sparked by weekend lightning strikes. Authorities say it spread quickly Sunday and Monday to threaten houses, a natural gas pipeline and a transmission line in remote southeast Treasure County