Search crews fanned out across the vast backcountry of the Great Smoky Mountains National Park on Friday after severe thunderstorms the night before killed two people and injured eight, park officials said.

An unknown number of hikers and campers may have weathered the Thursday night storm on the dozens of trails and isolated primitive camping sites in the most hard-hit western portion of the park, spokesman Carey Jones said Friday morning.

"We have no idea how many people are in the backcountry," he said. "We're just now getting people onto trails."

Officials have no indication that anyone was hurt or is in distress in the most isolated portions of the park, which straddles the border between Tennessee and North Carolina. But the park's backcountry has no cellular telephone service, and the storm hit during a busy time, noted Chief Ranger Clayton Jordan.

Jordan identified the dead as Ralph Frazier, 50, of Buford, Georgia, and 41-year-old Rachel Burkhart of Corryton, Tennessee.

Frazier, who was on a motorcycle, died when a tree limb fell and struck him on the head, Jordan said. A passenger on the motorcycle was not injured, Jordan said.

Jordan said Burkhart died when she was struck by a tree at a popular swimming hole near the park's Abrams Creek campground.

She was apparently among a number of swimmers who were scrambling to get out of the water when the storm roared through and toppled a tree that knocked them back into the water, Jordan said.

Three members of another family were also injured in the incident, including a 7-year-old girl who was trapped under water by the tree, Jordan said. Bystanders performed cardiopulmonary resuscitation and revived the girl, Jordan said.

She and her father -- who sustained serious injuries including back injuries, broken ribs and a collapsed lung -- were flown to the University of Tennessee Medical Center in Knoxville. The girl's mother was also injured, but less seriously, and was taken by ambulance to the same hospital, Jordan said.