The pair, who were lifelong Newcastle fans, were flying out to New Zealand to watch the Magpies play in their upcoming pre-season tour.
"Myself and all the players are deeply shocked and saddened by this terrible news," Pardew told the club's official website. "We all knew how passionately John and Liam supported the team and the club.
"They were with us just earlier this week for our first pre-season friendly against Oldham and 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. Our hearts go out to their families and friends."
Pardew and his players will wear black armbands as a sign of respect for the pair during their friendlies against Sydney FC and Wellington Phoenix.