SWEDESBORO, N.J. -- NASCAR driver Jason Leffler died after an accident Wednesday night in a heat race at a dirt car event at Bridgeport Speedway.

The 37-year-old Leffler, a two-time winner on the NASCAR Nationwide Series who had the nickname "LefTurn" above the driver's side window on his race cars, was pronounced dead shortly after 9 p.m. ET, New Jersey State Police said.

"NASCAR extends its thoughts, prayers and deepest sympathies to the family of Jason Leffler who passed away earlier this evening," NASCAR said in a statement. "For more than a decade, Jason was a fierce competitor in our sport and he will be missed."

Bridgeport Speedway immediately suspended racing for the rest of the night after Leffler's accident at the 0.625-mile, high-banked dirt oval.

Meanwhile, on Thursday, New Jersey State Police announced they are trying to determine the cause of the fatal crash.

After losing his NASCAR ride, Leffler had been racing dirt car events most of this year, including the 410 Sprint Car race Wednesday that promised a $7,000 prize to the winner. On Sunday, Leffler finished last at Pocono in his lone NASCAR Sprint Cup start of the year. He ran just eight laps in a start-and-park ride.

From Long Beach, Calif., Leffler made 423 starts in NASCAR's three national series but won just the two Nationwide races and one Truck Series event in a career that began in 1999. He also made three IndyCar Series starts, finishing 17th in the 2000 Indianapolis 500.

A statement from Indianapolis Motor Speedway called Leffler "one of the most versatile race drivers in America, showing his talent by competing in the Indianapolis 500 and the Brickyard 400 at the Indianapolis Motor Speedway during his career."

"He also displayed the skills that would help him reach the top levels of the sport by winning four USAC national series titles while winning on tracks throughout the Midwest," the statement said.