A woman in Colorado has saved her five-year-old son by prying open a mountain lion's mouth after the animal attacked the boy in their front yard, officials say.

The mother heard screams and raced outside the house near Aspen, where she found the animal on top of her son, the Pitkin County Sheriff's Office said.

The boy suffered face, head and neck injuries and was said to be in fair condition at a hospital in Denver.

Officials said two lions were killed.

The unidentified woman said she grabbed one of the animal's paws and stuck her right hand in its mouth to pry it open and free her son's head, Pitkin County Sheriff's Deputy Michael Buglione said.

The mother had bite marks on her hand and scratches on her leg after the lion, believed to be two years old, ran off, he added.

Wildlife officials said they killed a young lion near the home and a second one found in the area several hours later.

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The incident happened on Friday night in the community of Lower Woody Creek, north of Aspen.

Officials say sightings are increasing across Colorado, where an estimated 4,500 mountain lions live.

The last known mountain lion attack in the state happened in July 2015 when a young animal attacked a man as he fished in a remote area in northwest Colorado, the wildlife department said.