A dog bit off a four-year-old boy’s hand and part of his arm after he tried to play with the animal under a fence.

The youngster had a sock on his arm when he stuck it in a gap between the ground and a fence in the back garden of his home in Utah on Sunday.

The husky on the other side of the partition bit the child’s entire hand and two to three inches of his arm off.

The youngster was flown by helicopter to hospital where he had surgery, Layton Fire Battalion chief Jason Cook said.

Authorities believe the dog ingested the boy’s hand, which they have been unable to find.

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Mr Cook said medical staff and animal control officials briefly considered putting the dog down to retrieve the hand and attempt to reattach it, but a surgeon determined it was not an option.

The boy is said to be recovering well.

Rhett Nicks, director for Davis County Animal Care and Control, said the husky would be quarantined for 10 days.

Officials have not yet decided whether the dog will be put down or listed as a dangerous dog and an investigation is underway, he added.

It was said to be the animal’s first reported bite, according to Mr Cook.

Animal control is holding another husky which lives at the house but was not involved.

The dogs were properly fenced in at the house in Layton, a city of about 80,000 residents about 25 miles north of Salt Lake City.

Mr Cook said he did not know if the boy was right-handed or not but that he should be able to adapt because he was so young.

He said: “He’ll kind of grow into his dexterity but it’s certainly life-changing.

“It’s just a sad turn of events for the young, little guy.”

Last year, a 17-month-old girl in Wiscasset, Maine, was severely injured when her baby sitter’s boxer bit her face after she touched its back.

The eight-year-old dog was taken in for a 10-day quarantine following the mauling.