Two friends on a morning mountain bike ride 30 miles (48 kilometres) east of Seattle were attacked by a cougar, killing one of the men and leaving the second hospitalised.

The cougar was later found up a tree near the dead man's body, where agents for the state's Fish and Wildlife police shot and killed it hours after the Saturday attack, the Seattle Times reported.

The names of neither man were immediately released.

The 31-year-old survivor said he and his friend were mountain biking in the Lake Hancock forest area at about 11am when they realised they were being chased by the big cat.

"So they stopped and they made a lot of noise, said Capt. Alan Myers of the state department of Fish and Wildlife, ''which is exactly what we counsel people to do.

"The two victims then took a minute and were catching their breath about this amazing, incredibly scary event that just occurred and suddenly the victim (the survivor) was attacked again by this cougar.

"It latched onto his head. He said he had his whole entire head in the jaws of this animal and was being shaken around very, very horribly."