Race officials said 14 fans were sent to nearby hospitals and another 14 were treated at the Florida track, which will host the prestigious Daytona 500 race on Sunday.
"Stuff was flying everywhere," spectator Terry Huckaby, whose brother was sent to the hospital with a leg injury, told the ESPN sports network. "Tires were flying by and smoke and everything else."
Among the injured were a 14-year-old boy in critical but stable condition, and a man who was in surgery for a life-threatening head injury, according to ESPN.com.
In Image: Tim George Jr. (5), Max Gresham (8), Brennan Newberry (14) and others get caught up in a crash as Norm Benning (57) and Ross Chastain (19) try to avoid the mess during the NASCAR Truck Series auto race at Daytona International Speedway, Friday, Feb. 22, 2013, in Daytona Beach, Fla.