More than 150,000 people signed an online petition to save the lives of two husky dogs bit a four-year-old boy in Utah causing doctors to amputate his arm.

The incident took place on Sunday when the boy was playing in the backyard of his family home in Layton and reached through the fence and into the neighbours' backyard where the two dogs—Polar and Bear—were, law enforcement said.

Jason Cook, the Battalion chief at Layton Fire Department, told NBC News that the child wore a sock on his arm when one of the dogs bit him so hard it ripped off a part of his limb.

The boy, while in stable condition, was subsequently airlifted to a hospital and underwent surgery to amputate his arm. Mr Cook said he “never been a part of a call like that” throughout his 29-year career in the fire department.

The dogs are currently quarantined in Davis County Animal Control as law enforcement investigates the incident.

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Davis County Animal Control Director Rhett Nicks believes it is likely for the dogs to be euthanised based on the severity of the boy’s injury.

“We are doing a dangerous dog investigation, which could range from nothing being done up to euthanasia,” Mr Nicks told an NBC affiliate.

Animal lovers are fighting back. Jessica Nusz, a best friend of Polar and Bear’s owner, created a Care2 petition to spare the dogs’ life who were involved in an “unfortunate accident.”

She said the dog thought it was playing with a toy, “bit down too hard and didn’t see that there was a child on the other side of the fence.”

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“This situation is unfortunate on both sides,” the petition reads. “And now both dogs are in quarantine at Davis county animal control. There are fears that Bear might be put down and he doesn’t deserve to be put down for this freak accident.”

More than 160,000 people signed the petition as of Thursday morning.