A man visiting a Wyoming national park was nearly mauled to death after a surprise run-in with two grizzly bears.

The 35-year-old Massachusetts man suffered serious injuries Sunday at Grand Teton National Park in Moose, Wyoming, according to the National Park Service.

"Based on initial reports from the injured visitor and preliminary information conducted as part of an ongoing investigation of the site, law enforcement rangers and park biologists believe the incident was a surprise encounter with two grizzly bears, with one of the bears contacting and injuring the visitor," park officials said.

The victim was airlifted out of the park and transported via ambulance to a local hospital, where his condition is stable.

The attack prompted the closures of Signal Mountain Summit Road and Signal Mountain Trail.

In order to prevent bear attacks, the NPS advised visitors make noise, carry bear spray, and hike in groups of three or more. If a bear is encountered, park officials say to back away slowly.

"Do not run," officials advised.