DAYTONA BEACH, Fla. — At least 33 fans were injured Saturday during a NASCAR race when a car flew into the fence at Daytona International Speedway, hurling a tire and large pieces of debris into the stands.

The accident happened on the final lap of the second-tier Nationwide Series race on the eve of today’s 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 went airborne into the fence.

The 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.

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

“It was freaky. When I looked to my right, the accident happened,” said Rick Harpster of Orange Park, Fla., who had a bird’s-eye view of the wreck. “I looked over and 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. I knew it was going to be severe.”

Speedway President Joie Chitwood said 14 fans were treated on site, and 14 others were taken to hospitals. Chitwood didn’t give updates on their conditions. Local officials said 19 fans were taken to neighboring hospitals, including two who arrived in critical condition but were later listed in stable condition.

The accident happened the day before the Sprint Cup Series season-opening Daytona 500. Track workers could be seen repairing the large section of fence where Larson hit, as well as the wall that was damaged.

“First and foremost, our thoughts and prayers are with our race fans,” Chitwood said.

“We’re in the process of repairing the facility and will be ready to go racing (today).”

As emergency workers tended to injured fans and ambulance sirens wailed in the background, a somber 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.

“We’ve always known, and since racing started, this is a dangerous sport,” said Stewart, the three-time NASCAR champ. “But it’s hard. We assume that risk, but it’s hard when the fans get caught up in it. ...

“I could see it all in my mirror, and it didn’t look good from where I was at.”

It was a chaotic finish to a race that was stopped for nearly 20 minutes five laps from the finish by a 13-car accident that sent driver Michael Annett to a hospital, where his Richard Petty Motorsports team said he would be held overnight with bruising to his chest.

The accident ended the race for Irmo native Danny Efland on lap 116 out of 120. Efland finished 25th after starting from the 38 spot.

Afterward, Efland tweeted, “Sad day for MotorSports. Praying for our fans.”