A wildfire that started Friday on National Forest land southwest of Sheridan, Wy., has nearly doubled in size since last night, a federal fire official said.

The fire now stands at 4,200 acres, up from 2,500 acres Sunday night, said Steve Segin, U.S. Forest Service spokesman for the Rocky Mountain region.

"It's spreading fast. The hot and dry weather is going to make it hard and difficult" to contain the fire, he said.

Segin said the fire has already destroyed two structures and damaged a third.

He said people in the area have been evacuated. The number of evacuees wasn't immediately available.

There are no reports of injuries.

Segin said the fire is zero percent contained. Last night, County Road 26 was closed and evacuations were under way. Segin didn't now if the road was still closed at noon today.

The fire has been designated a Type 2 fire, which means resources from nearby states can be called to assist, Segin said.

He said more than 100 firefighters and fire personnel from the U.S. Forest Services are helping.

Bill Crapser, Wyoming state forester, said today that the Little Goose Fire had threatened about 100 homes and cabins in the area, about 15 miles southwest of Sheridan.

Crapser said a federal fire management team is directing the firefighting efforts. He said the state is seeking federal funds to help fight the fire.

Crapser said there are 10 engines and three helicopters assigned to the fire, as well as hand crews. He said the state isn't sure yet whether the structures that burned are summer cabins or permanent residences.

He said weather conditions are very dry across central Wyoming.

Associated Press contributed to this report.