ATOMIC CITY, Idaho -

A fire burning four miles southwest of Atomic City is burning 600 acres, the Bureau of Land Management said Wednesday morning.

The Midway Fire is south of the junction of highways 20 and 26.

The blaze started around 5:30 p.m. Tuesday. The fire perimeter is 20 percent active, although that may change as temperatures rise, and fuels dry and become more burnable.

The fire appears to be stalled, to some extent, in lava flows.

There are structures threatened four miles north of the fire. So far, no evacuations are expected.

Ten engines, three dozers, four single-single air tankers and an air attack platform are being used to fight the flames. Rough terrain and limited access are hindering firefighting efforts.

Lightning sparked this fire.