Three people are still in intensive care after becoming ill while taking part in the Nijmegen Vierdaagse, a four-day marching event, the AD said on Thursday afternoon. One of them had to be reanimated.
A fourth walker who was taken to intensive care has since been released, the paper said.
In addition, six walkers were admitted to hospital with heat stroke and several dozen others have been treated in accident and emergency departments. Some 2,000 of the 44,000 walkers dropped out of the event on Wednesday, which was the hottest day of the year so far.
Friday is the final day of the Vierdaagse, which celebrates its 100th anniversary this year.