A grizzly bear with her cub attacked several teens participating in a wilderness survival skills course in Alaska, badly mauling two in the group, state troopers said Sunday.

A grizzly bear, perhaps being protective of her cub, attacked several teens taking part in a wilderness survival course in Alaska on Saturday. (Associated Press file photo)The teens were among seven students participating in a 30-day backcountry course by the National Outdoor Leadership School when the attack occurred Saturday night in the Talkeetna Mountains north of Anchorage. They were rescued early Sunday.

The teens told troopers the attack occurred as they were lined up for a river crossing. Those in the back of the line heard screams about the presence of a bear, with the two at the front of the line taking the brunt of the attack, trooper spokeswoman Megan Peters said.

Another group of seven students and three instructors was waiting about 10 kilometres away for a helicopter hired by the Lander, Wyo.-based NOLS, said Bruce Palmer, a spokesman for the organization, which leads many such excursions in Alaska and elsewhere.

Joshua Berg, 17, of New City, N.Y., and Samuel Gottsegen, 17, of Denver suffered the worst bites, Palmer said. They were being treated at Providence Alaska Medical Center in Anchorage, where hospital spokeswoman Crystal Bailey said both are listed in serious condition.

Two others also were injured, Palmer said.

Victor Martin, 18, of Richmond, Calif., was taken to Mat-Su Regional Medical Center in Palmer, about 60 kilometres northeast of Anchorage, and released after being treated for a bite wound above his ankle, according to Palmer. Noah Allaine, 16, of Albuquerque, N.M., remained at the hospital listed in good condition, according to hospital spokeswoman Margo Wesley.

The teens were in the 24th day of their course when the attack occurred. There was no instructor with them because that far into the course, they've learned enough survival skills, Palmer said.

"Our basic goal is that when a student graduates from the NOLS course, they have the experience and background to be able to take other people out into the backcountry," he said. "We're training people to be outdoor leaders basically."

Calling out to warn bears is among the skills learned in the course. "The students say they were" [doing that], Palmer said.

The teens told troopers the 8:30 p.m. attack occurred as they lined up in single file for a river crossing. The bear attacked Berg first, turned to another student, then turned back to Berg, Palmer said.

After the attack, the teens applied first aid to each other, set up camp and activated a personal locator beacon they carried to be used only for an emergency, Peters said.

The Rescue Coordination Center operated by the Alaska Air National Guard called troopers around 9:30 p.m. to report the activated locator signal. A trooper and pilot in a helicopter located the students in a tent shortly before 3 a.m., but decided the two most seriously injured couldn't safely be flown in the helicopter, but would need a medical transport aircraft with a medically trained crew.

They called the rescue centre for help and the helicopter pilot flew four of the teens to the Talkeetna airport. From there, they were driven by ambulance to the hospital in Palmer, where they were checked.

The trooper and another student stayed with the badly injured teens for four hours until more rescuers arrived in a specially equipped helicopter, which flew them to the Anchorage hospital, Peters said.

The uninjured student who remained is Samuel Boas, 16, of Westport, Conn. Palmer said Boas has training as an emergency medical technician.