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A police statement said the vehicle drove away from the scene and is being sought. Other media reports described the vehicle as a small white bus.
The incident took place at the "PinkPop" concert, a popular festival being held in Limburg province in the south of the Netherlands.
A police statement said the street where the incident took place, one of two exits from the concert grounds, had been closed for investigation.
"The bus is being sought," the statement said.
An alert service sent by emergency authorities to cell phones in the area warned people to be alert for a Fiat Doblo with the number 257 as part of its licence plate.
RTL news reported that a trauma helicopter, ambulances and a heavy police presence were at the scene.
Bruno Mars was the headline act that closed the three-day concert on Sunday night, hours before the incident took place.