A bear grizzly attacked a group of teenage hikers deep in the wilderness of Alaska's Talkeetna Mountains on Sunday, causing severe injuries to two of the seven hikers.

The hikers were crossing a stream single file when the grizzly, a mama bear with a cub, ambushed the hiker at the front of the line. He started screaming as the bear began biting and clawing him before moving to another teen.

The group was on the 24th day of a 30 day wilderness survival course taught by the National Outdoor Leadership School. It was the first day hiking without an adult instructor for the teenagers, all of whom were between 16 and 18 years old.

"For the last bit of the course, we would have them travel as a student group without the instructors, utilizing the skills that they've learned over time," school spokesman Brian Palmer said.

After the attack, the hikers administered first aid to their two badly wounded comrades as they signaled for help with a locator beacon. The Alaska Air National Guard dispatched a helicopter, which arrived at about 2:45 AM.