Two young sisters who were believed to have been held by a religious cult leader in Utah have been found hungry, cold and alone in a storage receptacle – with officials saying had they not been discovered, they may not have lasted the night.

Four-year-old Hattie Coltharp and eight-year-old Dinah were found outside the town of Lund on Monday night (4 December). Their brothers, William, 7, and Seth, 8, had been found safe earlier the same day.

It comes after an Amber Alert was issued when their mother, Micha Soble, said her four children had disappeared on 13 September.

Their father, John Coltharp, 33, who does not have custody, is accused of kidnapping the youngsters and trying to raise them in a fundamentalist Mormon sect called Knights of the Crystal Blade.

He was arrested last week but had refused to disclose the location of his children, even after prosecutors offered him a deal if he told them where they were.

Authorities then raided the shipping container compound of the polygamist sect, of which the father was a member.

The two boys were found during the raid, while the girls were later discovered within five miles of the compound following a tip off.

The Iron County Sheriff's Department said it was unlikely the two sisters would have survived the night had they not been found.

"They were shaken, but as they got warmer, they became much more calm and talkative," Lt. Del Schlosser said.

Samuel Warren Shaffer, 34, who sees himself as a prophet for Knights of the Crystal Blade, has also been taken into custody.

Soble, Coltharp's ex-wife, described her former husband as a "doomsday prepper" – a term for someone preparing for apocalyptic scenarios.

When married they had been members of the Latter Day Saints Church but he was excommunicated for his extreme beliefs, Soble told the Denver Post.

In divorce papers filed after he and her children disappeared, she said he didn't trust modern medicine and wouldn't even allow her painkillers during child birth.

She added that he had "threatened to send any DCFS [Division of Child and Family Services] worker or police officer to the next life if they try to take the children from him."

Coltharp's sister, Cindi Ray, said her brother had also said he believes girls should be married from the age of 12 because "their bodies are ready".

Coltharp is being held on a $100,000 cash bond.