Ottio signed for Widnes at the end of previous year from Australian National Rugby League team the Canberra Raiders.
Ottio had been awaiting a visa to travel to Britain and was training with the local PNG Hunters side when he collapsed at training over the weekend.
Papua New Guinea worldwide 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.
The centre was part of the PNG side that lost to England in November's World Cup quarter-finals.
Canberra coach Ricky Stuart said: 'Receiving the devastating news this morning knocked me for six.
"Wasn't a day he wasn't smiling, gone way too soon", Austin wrote.
He was the NSWRL's leading tryscorer in 2016 while playing for Raiders feeder club the Mounties.
"But Kato told a few of the players "let's run back" - he wanted to use the professionalism he gained from his time at Canberra to rub off on his younger countrymen. Kato was an incredibly talented player, with a bright future ahead of him in rugby league", Rule said.
The players were clearly distraught and Marum said many of them would need support, including Albert, who was due to share a house in Widnes with Ottio.
"We are devastated to learn that Kato Ottio has passed away this afternoon".
Born on 20 March 1994 in Tatana near Port Moresby - the capital of his native Papua New Guinea - Kato Ottio made a name for himself as a volleyball and Rugby Union player rather than on the Rugby League field in his early life. They have to go through proper counselling through our pastor.
"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".
"It was hard to believe given the age of Kato and how I remembered him here".