The status of the driver wasn't released. Multiple witnesses described him as an elderly man.
Authorities are still investigating, but Harris said they believe the man might have suffered a medical emergency before the accident.
It happened around 2:30 p.m. during the Hikers Parade at the Trail Days festival, an annual celebration of the Appalachian Trail in Damascus, near the Tennessee state line about a half-hour drive east of Bristol.
What caused the car to drive into the crowd wasn't immediately known. It appeared to come from a side street, and a thud could be heard. People yelled stop, and at some point, the car finally stopped.
Witnesses said the car had a handicapped parking sticker and it went more than 100 feet before coming to a stop.
"He was hitting hikers," said Vickie Harmon, a witness from Damascus. "I saw hikers just go everywhere."
Damascus resident Amanda Puckett, who was watching the parade with her children, ran to the car, where she and others lifted the car off those pinned underneath.
"Everybody just threw our hands up on the car and we just lifted the car up," she said.
Keith Neumann, a hiker from South Carolina, said he was part of the group that scrambled around the car. They pushed the car backward to free a woman trapped underneath and lifted it off the ground to make sure no one else was trapped. Another person jumped inside to put it in park.
"There's no single heroes. We're talking about a group effort of everybody jumping in," he said.
There were ambulances in the parade ahead of the hikers and paramedics on board immediately responded to the crash.