The children, a girl and four boys, all died in the fire at a home in Bullhead City, Arizona, on Saturday.

Four of the victims, the girl, four, and three of the boys, aged two, five, and 13, were siblings.

The fifth child, an 11-year-old boy, was a family relative and was visiting at the time.

The father of the four children told investigators he had left them in the house for around two and a half hours while he went shopping for food and Christmas gifts, according to Bullhead City Police Department.

There was no other adult at the home at the time, according to police.

Because the victims are the grandchildren of a Bullhead City Fire Department employee, teams from Lake Havasu City Fire Department and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives have been brought in to help the police's investigation.

Investigators believe the fire started downstairs and travelled up the only staircase inside the home, preventing the children from exiting.

Several neighbours reportedly placed an extension ladder to the upstairs bedroom, but were unable to get the children out.

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Police said the five bodies were located in the same upstairs bedroom of the home, which is near the Colorado River and the Nevada border.

Their names are being withheld pending official identification by the Mohave County Medical Examiner's Office.

Bullhead City Police Chief, Robert Trebes, said investigators were "working tirelessly to get answers" about the fire's cause and "bring some closure and peace to parents and families involved".