A mountain biker has been killed and another mauled after straying into mountain lion territory in Washington state in the United States.

The cyclists were riding together down a remote, backwoods trail at 11am local time around 30 miles east of Seattle, when the two men encountered the animal.

In the ensuing attack, the first rider received deep scratches and the other was dragged away by the cougar to its den, King County Sheriff’s Office spokesman Sergeant Ryan Abbot said.

“He or she, I don’t know if the cougar was a male or female, had the body of the victim down in his den,” he added.

Police drove up the trail, found the victim’s bike and went into the woods where they came across the cougar standing over the victim’s body, Reuters reported.

The 31-year-old survivor rode two miles out of the area and called 911.

Abbot added: “They did everything they were supposed to do. But something was wrong with this cougar.”

A deputy took a shot at the animal, sending it fleeing into the woods. Officers of the Washington Department of Fish and Game tracked the cat with dogs and killed it, Abbott said.

The survivor was taken to hospital in Seattle with serious but none-life-threatening injuries, he said.

Fatal cougar attacks are extremely rare in North America, with only about two dozen recorded in the last 100 years, most of them involving children.

It was only the second deadly attack by a mountain lion in Washington State in the last 100 years, Abbott said.

Cougars are the fourth largest cat species worldwide, with adult females weighing up to 141 pounds (64 kgs) and males weighing as much as 220 pounds (100 kgs). They attack prey by ambush and usually attack humans only if cornered.