Replica jerseys and flowers were left outside Newcastle's St. James' Park after the team named the fans on Thursday's Amsterdam to Kuala Lumpur flight as John Alder and Liam Sweeney. Ages were not given.
"Myself and all the players are deeply shocked and saddened by this terrible news," Newcastle manager Alan Pardew said. "We all knew how passionately John and Liam supported the team and the club."
Alder was a "familiar sight in the stands for almost half a century, having barely missed a single game in that time," the northeast club said, adding that Sweeney volunteered as a steward on supporters' buses.
They were going to watch Newcastle's preseason tour matches in Dunedin and Wellington, where Pardew and his players will now wear black armbands.
"Their dedication to travel all the way around the world to support us in New Zealand tells you all you need to know about the passion they had for Newcastle United," Pardew said.