The Papua New Guinean centre – who faced England in the World Cup quarter-finals in November – had yet to arrive in this country after signing for the Vikings after the tournament.
Widnes chief executive James Rule said: “We are devastated to learn that Kato Ottio has passed away this afternoon.
“Kato was an incredibly talented player, with a bright future ahead of him in rugby league.
“This news is all the more tragic, because Kato was due to travel to the UK this week to fulfil his dream of playing first-grade rugby league.”