"Unfortunately attempts to revive [him] were unsuccessful and after 40 minutes the man was pronounced dead at the scene. Our sincere condolences go out to the family at this tragic time," he said.
Challenge media manager Nathan Cox said the man was from Whangarei and organisors were not yet naming him as family members were still to be told of the death.
Up to 150 cyclists were riding in the challenge, including cyclists from Wairarapa.
He said riders ranged in age from 18 to 74 and all had stayed overnight in Masterton on Sunday before setting out in two groups from the town yesterday.
He said cyclists made it by about lunchtime yesterday to Pahiatua, leaving at 1.30pm for Palmerston North.
The seven-day event started in Lower Hutt on Saturday with the 13th and final stage ending in Pukekohe on February 16.