Pocono spokesman Bob Pleban says it's not clear if all 10 were actually struck by lightning. It's unknown whether one or multiple lightning strikes occurred.
Pleban says five people were treated at the scene. He says one person was taken to Pocono Medical Center and another to Lehigh Valley, where they were in critical condition. The conditions of the other three are unknown.
The race was called because of rain, with 98 of the 160 scheduled laps completed.
The track posted warnings on its Twitter page near the end of the race encouraging fans to "seek shelter as severe lightning and heavy winds are in our area."
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