A teenager awoke to the "crunching noise" of a bear chomping down on his head, but nonetheless survived after the creature tried to drag him away.

The 19-year-old, named only as Dylan, was left with large gashes on his face and head after the creature tried to drag him out of his sleeping bag at around 4am on Sunday night.

The attack happened at Glacier View Ranch in Boulder County, where the teenager teaches wilderness survival.

Dylan punched and hit the bear as it dragged him, while other people sleeping nearby yelled and swatted the animal, which eventually left, a spokesperson for Colorado Parks and Wildlife said.

“The crunching noise, I guess, was the teeth scraping against the skull as it dug in,” Dylan said.

He told KMGH-TV he was dragged 10 to 12 feet away by the bear before he was able to free himself.

"That was the slowest part," he said. "It felt like it went forever."

Dylan and others had been sleeping near teepees where 12 and 13-year-old campers were situated. None of them were hurt in the attack.

Dylan was treated in hospital and released just six hours after the attack.

Colorado Parks and Wildlife spokesperson Jen Churchill said they had made finding the bear a priority.

“This is a bear that could be a continual threat to people in this community and we need to make sure that the animals have a healthy natural fear of human beings,” she said.

Black bears aren't usually aggressive but have attacked several people in the America in recent weeks. They will defend their young and have been known to paw and bite tents with food inside.

After the Colorado attack wildlife officers did not find any food that would have attracted the bear. They have set bear traps in the area and plan to continue a search for the animal with scent dogs.

The bear's behaviour was so atypical that any bear found in the traps in the next few days will likely be euthanised and officials will test later to see if it was the same bear involved in the attack using DNA evidence, Ms Churchill said.