One stock car racing fan was killed and nine others injured, one critically, when lightning struck at a track in Pennsylvania, officials said.

Multiple lightning strikes occurred behind the Pocono Raceway track's grandstands and outside one of the gates as fans were leaving the Nascar event in Long Pond, spokesman Bob Pleban said.

It was not immediately clear how many of the fans were actually struck by the lightning itself or were injured by related jolts.

"Unfortunately, a member of our raceway family here, a fan, has passed away," Pocono president Brandon Igdalsky said. He provided no details about the victim but expressed condolences to his family.

Mr Igdalsky later posted on Twitter: "My family and I are praying for all those that were involved in the lightning strikes... Difficult evening for all."

The Pennsylvania 400 was cancelled because of storms, with 98 of the 160 scheduled laps completed.

As the storm approached, the track posted messages on its Twitter page to more than 22,000 followers near the end of the race encouraging fans to "seek shelter as severe lightning and heavy winds are in our area".

The attendance was estimated by the track at 85,000. Public address announcements were made before the storm and the end of the race for fans to take shelter and evacuate the grandstands, Mr Pleban said.

Racetrack officials were reviewing the logs of when the announcements were made, he said. There was no order to evacuate the track premises.

Jeff Gordon, who won the race, said at a post-race news conference that he could hear a huge crack as he walked down the pit road during the storm.

"You could tell it was very close," he said. "I mean, that's the thing that's going to take away from the victory, is the fact that somebody was affected by that."

Kyle Manger, a spectator from New Jersey, told The Sporting News that he saw people hit by lightning near the Turn 3 grandstands.

He said when the severe weather began, he and some friends ran to their truck.

"The visibility was very poor and all of a sudden (I) saw a bolt of lightning right in front of our windshield," he said. "When it became a little more visible, we saw two bodies next to a destroyed tent with people scrambling."