A pile-up at the Daytona speedway circuit in Florida last night injured at least 28 fans and a driver after the 10-car crash sent car debris flying into the crowd.
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 today.
"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.
Driver Michael Annett of the Richard Petty Motorsports team was being treated at the Halifax Health Medical Center in Daytona Beach for bruises to his chest and sternum.
He was given a CT scan and was being kept for observation, the team said in a statement.
Joie Chitwood, president of the Daytona International Speedway, said today's main race would go ahead despite the incident as crews were repairing the track and the grandstand.
"First and foremost, our thoughts and prayers are with our race fans," Mr Chitwood said.
"Following the incident, we responded appropriately according to our safety protocols and had emergency medical personnel at the incident immediately."
Last night’s collision happened after driver Regan Smith, who was leading the race, attempted to block another driver as they were nearing the chequered flag and hit the other car, a report on NASCAR.com said.
"My fault," Mr Smith, who finished 14th, told NASCAR.com. "I threw a block. I'll take the blame for it. But when you see the chequered flag at Daytona, you're going to block, and you're going to do everything you can to be the first car back to the stripe.
“ It just didn't work out today. Just hoping everything is OK, everyone who was in the wreck and all the fans."
The crash sent driver Kyle Larson's car airborne and ripped out its engine, although he climbed out of the wreckage afterward unhurt.
"I was getting pushed from behind, it felt like," Mr Larson told ESPN after the crash.
"By the time my spotter said, ‘Lift, or to go low’, I believe, it was too late and I was in the wreck. Then I felt like it was slowing down, and it looked like I could see the ground, and had some flames in the cockpit. Luckily, I was all right and could get out of the car quick," he added.
The injured were taken to Halifax Health Medical Center and Florida Hospital Memorial Medical Center in Daytona Beach.
NASCAR's vice president of race operations, Steve O'Donnell, said the fencing, which was ripped through by the flying debris, was being replaced and the incident would be reviewed.
It is rare that spectators get hurt in American racing, but it has happened before. As recently as 2009, Carl Edwards' car slammed into the catch fencing at Talladega and injured nine fans.
Reuters