A man used a chainsaw to fight off an apparently starving mountain lion that attacked him during a camping trip in north-western Wyoming with his wife and two toddlers.

Dustin Britton, a 32-year-old mechanic and ex-US marine from Windsor, Colorado, said he was alone cutting firewood about 100ft from his campsite in the Shoshone national forest when he saw the lion staring at him from some bushes.

Britton said he raised his chainsaw and met the lion head-on as it pounced – a collision he described as feeling like a grown man running directly into him.

"It batted me three or four times with its front paws and as quick as I hit it with that saw it just turned away," he said.

Wildlife officials said the attack on Sunday evening was highly unusual because mountain lions are generally reclusive by nature. Only eight cases of mountain lions acting aggressively toward humans have been documented in Wyoming over the last decade.

"It's very, very rare" for lions to attack, said Wyoming game and fish spokesman Warren Mischke. "We're still trying to investigate why this lion would behave this way."

The wounded animal retreated after Britton inflicted a gash on its shoulder, leaving him with only a small puncture wound on his forearm.

"You would think if you hit an animal with a chainsaw it would dig right in," he said. "I might as well have hit it with a hockey stick."

After Britton's confrontation, he and his wife, Kirsta, decided to spend the night in their pop-up camper with their two children.

The lion was shot and killed on Monday after it attacked a dog brought in to track it. Authorities say it was in poor physical condition and appeared to be starving.

Tests for rabies and other diseases came up negative, but officials said they were continuing to analyse the animal for other potential diseases.