Debris from the crash flew as far as 20 feet into the stands. The engine from Larson's car flew free and lodged into the protective fence that separates the grandstands.
The 12-car wreck happened at the end of the Nationwide series NASCAR race in Daytona Beach, Fla.
CNN reports that several spectators were seen suffering from injuries after the crash but it was not immediately clear how serious the injuries were.
Photos from the scene showed people being carried away on stretchers.
"Right now, the function is to determine what damage was done," NASCAR president Mike Helton told ESPN.
"They are taking some folks to Halifax Medical Center. Our prayers and thoughts are with everyone they are working on."
Spectator Travis Smith witnessed the crash from inside the main grandstands.
"The damn car went through the fence. It shattered everywhere," he told USA Today. "Tires went flying everywhere. Hit a bunch of people."
"The last thing I remember, a tire was coming right at me," he added. "I turned my back and turned back around and it was panic. It was a sight to be seen."
Larson climbed out of the wreckage of his his car and was not hurt.
"I was getting pushed from behind," Larson said. "Before I could react, it was too late. Flames came in the cockpit, but I was able to get out of the car quick."