NASCAR officials sent drivers to the pits and instructed fans to clear the stands at Indianapolis Motor Speedway as severe weather entered the area during Sunday's Brickyard 400.
The race was stopped just 12 laps in. Pole-winner Kyle Busch led every lap and had built a lead of more than three seconds before the caution flag came out, preceding the rain and lightning.
About 35 minutes later, fans were allowed to re-enter the grandstands.
A NASCAR spokesman said only that racing would resume as soon as possible.
The race would become official after completing Lap 81, just beyond the midway point of the scheduled 160-lap event.