Ottio was expected to travel to England next week to get ready for the start of the new Super League season in February having signed for Widnes from Canberra in December.
The centre was part of the Papua New Guinea side which lost to England in November's World Cup quarter-finals.
James Rule, CEO of Widnes Vikings, told the team's official website: “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. We had been in regular contact with Kato and were excited to welcome a bright, excited and passionate young man, who had genuine potential for the future.
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"Widnes Vikings will of course be looking to celebrate Kato’s life and pay our sincere respects to someone who we believe would have become a hero at our club".
The club said they were "still learning the full facts of this situation".
(Reporting by Simon Evans, editing by Pritha Sarkar)
