Two big cats potentially involved in the suspected New Year's Day mauling were euthanized, state wildlife officials said.

At around 12:15 pm on Thursday, hikers on the Crosier Mountain trail in Larimer County spotted a mountain lion near a person lying on the ground, Colorado Parks and Wildlife (CPW) spokeswoman Kara Van Hoose said.

"As they started to get closer, they started to scare the lion from the area by throwing rocks at the animal, and it eventually went away," Van Hoose told reporters. "One of the witnesses is a physician, and did not find a pulse."

Wildlife officials, sheriff's deputies, park police and volunteer firefighters launched an extensive search -- joined in the air by a state biologist who was carrying out an annual deer survey by helicopter.

"We also contacted houndsmen to bring in dogs to help track scent from lions, which is a really effective way to find mountain lions," said Van Hoose.

One animal was shot at the scene but died only after fleeing, being rediscovered and shot again. A second lion near the scene was also killed, under state policy requiring any wildlife involved in human attacks to be euthanized to ensure public safety.

Mountain lions are highly territorial, making it likely only one was involved in the attack.

Pathologists will carry out necropsies on the animals, looking for neurological disease like rabies or signs of human DNA.

The county coroner will release the identity of the victim and cause of death.

Van Hoose stressed that mountain lion attacks are exceedingly rare, with only 28 reported since 1990 in Colorado, and the last fatality in 1999.

Mountain lions are more visible in winter as they follow deer and elk to lower elevations, she added. If lions are spotted, make noise to scare them, hold objects overhead to appear bigger and start backing away from the animal.

Colorado is home to roughly 3,800 to 4,400 mountain lions -- a figure that excludes kittens.

Once considered big game, their population has grown since 1965 as a result of supportive management practices.

Mountain lions have the widest geographic range of any native mammal in the Americas apart from humans, stretching from western Canada to Argentina. Previously found across the United States, they are now extinct or endangered in the east, with the western states forming their stronghold.

Adults are more than six feet (1.8 meters) long, weighing 130 pounds (60 kilograms) or more, with black-tipped tails. Their staple diet are deer, and they hunt by stealth often pouncing from trees or overhanging rocks.