Papua New Guinea international Ottio, who represented his country at last year’s World Cup, was due to travel to join Widnes for pre-season training after signing for them in December.
Widnes CEO James Rule said: “We are devastated to learn that Kato Ottio has passed away (Monday) 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.
“Having only learned this morning that Kato had developed a sudden health issue while training yesterday (Sunday), we are in absolute shock to now receive this tragic news.
“We will be liaising closely with his loved ones to offer them our condolences and support at this difficult time.
“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.
“Whilst we are coming to terms with this news, and still learning the full facts of this situation, we are unable to comment further at this time.”
Head coach Dennis Betts added: “All of us saw at the World Cup the incredible gifts that Kato had, and his potential to forge a great career in rugby league.
“Moreover, in all of our interactions with him, we found Kato to be a person of great character, who was excited to be following his dreams.
“On behalf of the coaching team, staff and players at Widnes Vikings, I would like to offer our sincere condolences to Kato’s loved ones.”