UPDATE: Tony Stewart Out of Sunday's Race after Hitting, Killing Other Driver

Greg Zipadelli has announced that Tony Stewart will not race today. Regan Smith will run the #14 car today at Watkins Glen.

(CANANDAIGUA, N.Y.) - Tony Stewart struck and killed a fellow driver with his sprint car late Saturday night during a dirt-track race at Canandaigua (N.Y.) Motorsports Park, the Ontario County Sheriff's Department announced early Sunday morning.

Greg Zipadelli has announced that Tony Stewart will not race today. Regan Smith will run the #14 car today at Watkins Glen.

Earlier, according to multiple reports, Stewart-Haas Racing Vice President of Competition Greg Zipadelli says Stewart will race in Sunday's NASCAR Sprint Cup event. According to The Associated Press, Zipadelli called the race "business as usual."

In the sprint-car incident, Sheriff Philip Povero confirmed the driver, whom Povero would not identify, was dead on arrival to an area hospital Saturday night and that Stewart was the driver who struck him. He said that his department's investigation is not criminal and that Stewart was "fully cooperative" and appeared "very upset" over what had happened.

Povero said the driver was pronounced dead Saturday night at a Canandaigua hospital. Stewart was unhurt. While Stewart is being investigated, Povero said the investigation is not criminal and that no charges have been filed. Stewart was released; the three-time Sprint Cup champion is believed to be in Watkins Glen, N.Y., for Sunday's Sprint Cup race.

According to multiple reports, Stewart was involved in an on-track incident with 20-year-old driver Kevin Ward Jr., with Stewart's car striking Ward after he got out of his car to confront Stewart about earlier contact between the two. Late Saturday night, video of the incident was posted on YouTube. In it, shocked fans sob and scream after Stewart runs over another driver and that driver lies motionless on the track while emergency personnel respond.

You can hear the motor rev just before the car hits the driver, who flies about 50 feet.

"People that witnessed it were horrified," Povero said of the crash, according to AP. "They were extremely shocked."

Povero said the the 25-lap race was under caution when Ward was struck. Stewart's car was behind another before he hit Ward.

Tyler Graves, a sprint-car racer and friend of Ward's, told Sporting News in a phone interview that he was sitting in the Turn 1 grandstands and saw everything.

"Tony pinched him into the frontstretch wall, a racing thing," Graves said. "The right rear tire went down, he spun on the exit of (Turn) 2. They threw the caution and everything was toned down. Kevin got out of his car. … He was throwing his arms up all over the place at Tony for most of the corner.

"I know Tony could see him. I know how you can see out of these cars. When Tony got close to him, he hit the throttle. When you hit a throttle on a sprint car, the car sets sideways. It set sideways, the right rear tire hit Kevin, Kevin was sucked underneath and was stuck under it for a second or two and then it threw him about 50 yards."

"You never mean to do something like that," Graves told Sporting News. "Kevin was pissed and he let Tony know. And Tony was trying to give the message back that he wasn't happy either. He went over the line with it."

Video of the crash showed Ward, in the No. 13 car, spin into a wall after contact with Stewart's car. Ward, wearing a black firesuit and black helmet, climbed quickly from his car and briskly walked around it in what appeared to be an attempt to confront Stewart as he passed by in his own car, his familiar No. 14.

The video showed Ward to the right of Stewart's car, which seemed to kick out from the rear and hit Ward. The driver was hurtled through the air and emergency personnel quickly reached Ward as he lay on the track.

Michael Messerly, a fan who witnessed the crash, told The Associated Press it appeared Stewart struck the driver as he tried to "speed past" him.

"I didn't see (the other driver) anymore," he said. "It just seemed like he was suddenly gone."

Messerly said the crash appeared to be the result of "a number of bad decisions" and not "any intent on Tony Stewart's part."

"Auto racing is a dangerous sport," he said. "I think it was just an unfortunate set of circumstances that created a tragic situation."

After the incident, racing for the evening was cancelled, police were dispatched and fans were told to leave the track. The sheriff is asking for people who have video of the crash to contact the office so copies can be obtained for review.

Stewart was involved in a July 2013 accident at Canandaigua Motorsports Park that seriously injured a 19-year-old driver. He later took responsibility for his car making contact with another and triggering the 15-car accident that left Alysha Ruggles with a compression fracture in her back.

On Saturday, ambulances, fire trucks and police arrived within minutes of the crash, Messerly said. Fans filed out in stunned silence, he said.

The Ontario County Sheriff's Department says its officers were at the track investigating into the early morning Sunday.

Stewart, 43, only returned to sprint track racing last month, almost a year after breaking his leg in a crash at an Iowa track. The accident cost him the second half of the NASCAR season, and he didn't return to racing in any form until February when preparation for NASCAR's season-opening Daytona 500 began.

He refused to stop his extracurricular racing despite the injury and was scheduled to race Sunday. He's still planning to run the race, sources told the Charlotte Observer early Sunday morning.

Stewart was a spectator at the Knoxville Nationals in Iowa on Tuesday, the one-year anniversary of the accident, and posted on his Twitter account: "Thank you to everyone that worked so hard to get me back to where I'm at today. It's your life, live it!"

Roughly three hours after the accident in New York, Donny Schatz, a sprint car driver for Tony Stewart Racing, won the prestigious Knoxville Nationals in Iowa for an eighth time. Stewart had spent much of the earlier part of the week trackside in Iowa watching his drivers compete.

"I was just told there was an incident involving Tony. I don't know to what extent or what's happening," Schatz said.

Stewart, a three-time NASCAR champion, is co-owner of Stewart-Haas Racing, the four-team Sprint Cup organization that fields cars for Stewart, Kevin Harvick, Kurt Busch and Danica Patrick. He's struggled a bit this year since returning from his injury, and heads into Sunday's race winless on the season and ranked 19th in the standings.

Stewart was scheduled to start 13th on Sunday at Watkins Glen International in south central New York state. He has just five races remaining to either score a win or move inside the top 16 in points to grab a valuable spot in NASCAR's championship race.

Calls to Stewart's representatives were not immediately returned. Stewart-Haas Racing released this statement Sunday morning: "A tragic accident took place last night during a sprint car race in which Tony Stewart was participating. Tony was unhurt, but a fellow competitor lost his life. Our thoughts and prayers go out to his family and friends. We’re still attempting to sort through all the details and we appreciate your understanding during this difficult time."