UPDATE: The Sanpete Sheriff has issued mandatory evacuations for the area of Hideaway Valley south of Ridge Road, and west of Shadow Canyon Road as the Hilltop fire continues to burn.
Officials said just before 1 p.m Tuesday they determined the fire is human-caused, but specific details about how the fire began were not immediately available.
Officials said witnesses are being cooperative but did not elaborate.
Sanpete County Sheriff's Office stated that as of about 11:10 a.m. they are giving pre-evacuation notices in portions of Hideaway Valley.
Those in pre-evacuation notice areas are encouraged to monitor fire conditions and be prepared to leave at any time.
The sheriff's office states the Red Cross is expected to arrive in the area around 2:30 p.m. to create an evacuation receiving center at the Indianola Church.
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MILBURN, Utah -- At least 350 homes are under a mandatory evacuation order and some have been destroyed in the Milburn area as crews continue to battle the Hilltop Fire Tuesday morning.
As of Monday night the fire was estimated at about 1,400 acres, but fire officials say the thick and heavy smoke makes it difficult to make an accurate estimate of the size of the fire. There is no containment.
Tuesday morning officials said at least 150 structures were threatened as of Monday, and two of those structures have been lost. The fire burned actively all night and crews are making the protection of structures their top priority Tuesday.
As of Tuesday there are about 100 personnel on scene along with 16 engines, four dozers, one helicopter and one handcrew.
Fire officials say conditions were too dangerous for crews to fight the fire on the ground Monday. Aerial resources have been making water and retardant drops.
The evacuations are in the Black Hawk subdivision and in Milburn, and other nearby areas are on standby to evacuate. On Tuesday, the Sanpete County Sheriff's Office reported portions of Hideaway Valley have been placed on pre-evacuation notice.
"Pre evacuation means be ready to leave and pay attention to fire conditions," a tweet from the Sheriff's Office said.
Fire officials said Monday night that Milburn and Hill Top Roads are both closed.
Lt. Gov. Spencer Cox is from Fairview, about 6 miles south of Milburn, and was on hand Monday. He said things are tense but people are working together.
“It’s intense out there right now," he said. "This fire took off. It's going like crazy. The good news is we got everybody out."
Cox also highlighted the hard work of a relative, saying his cousin/drummer was working overnight Monday to help protect homes.
FEMA has authorized federal funds to pay up to 75% of fire fighting costs for the fire.
Fox 13 News will update this story as more details emerge.