At least 33 NASCAR fans were injured when a car flew into the fence at Daytona International Speedway on Saturday, hurling a tyre and large pieces of debris into the stands.

The accident happened on the last lap of the second-tier Nationwide Series race on the eve of Sunday’s Sprint Cup season-opening Daytona 500, which officials said would go on as scheduled.

The crash began as the field approached the checkered flag and leader Regan Smith attempted to block Brad Keselowski to preserve the win.

That triggered a chain reaction, and rookie Kyle Larson hit the cars in front of him and his car was went airborne into the fence.

The entire front end was sheared off Larson’s car, and his burning engine wedged through a gaping hole in the fence.

Chunks of debris from the car were thrown into the stands, including a tire that cleared the top of the fence and landed midway up the spectator section closest to the track.

The 20-year-old Larson stood in shock several yards away from his car as fans in the stands waived frantically for help. Smoke from the burning engine briefly clouded the area, and emergency vehicles descended on the scene.

Ambulance sirens could be heard wailing behind the grandstands at a time the race winner would typically be doing celebratory burnouts.

“I saw a tire fly straight over the fence into the stands, but after that I didn’t see anything else. That was the worst thing I have seen, seeing that tire fly into the stands,” said fan Rick Harpster, who had a bird’s-eye view of the wreck.

Shannon Speedway President Joie Chitwood said 14 fans were treated on site, while local officials said 19 fans were taken to neighbouring hospitals, including two who were in critical condition but were later upgraded to stable.

As emergency workers tended to injured fans and ambulance sirens wailed in the background, a sombre Tony Stewart skipped the traditional post-race victory celebration.

Stewart, who won for the 19th time at Daytona and seventh time in the past nine season-opening Nationwide races, was in no mood to celebrate.

“As much as we want to celebrate right now and as much as this is a big deal to us, I’m more worried about the drivers and the fans that are in the stands right now because that was … I could see it all in my mirror, and it didn’t look good from where I was at,” he said.