It is understood Ottio was training in Port Moresby with players from Queensland Cup side PNG Hunters when he collapsed after a long running session.
He was taken to hospital but fell into a coma and never recovered.
This news is all the more tragic, because Kato was due to travel to the United Kingdom this week to fulfil his dream of playing first-grade Rugby League.
Ottio was initially offered a train and trial deal with the Raiders, impressing the coaching staff enough to play in the Auckland Nines and secure a permanent contract.
The club said they were "still learning the full facts of this situation".
"We are devastated to learn that Kato Ottio has passed away this afternoon", Widnes chief executive, James Rule said.
He had six caps for his country and had played against England in the recent World Cup.
Ottio spent two seasons with the Canberra Raiders in Australia but after failing to break into their National Rugby League squad, which saw him sign with Widnes in December. "It was hard to believe given the age of Kato and how I remembered him here, I am really lost for words", Stuart said. My thoughts go out to his family.
It is thus with great sadness that Ottio never got to pursue his Super League ambitions and that Super League was never able to witness a player that had the devastating ability to light up the field like few before him.
Ottio signed for Widnes at the end of past year from Australian National Rugby League team the Canberra Raiders.
Widnes coach Denis Betts said he was yet to speak to Albert but the club would do whatever was necessary to support the former Penrith Panthers prop.
After signing for Canberra in early 2016 he established himself as a major part of feeder club Mounties, scoring regularly in NSW Cup fixtures.
'On behalf of the coaching team, staff and players at Widnes Vikings, I would like to offer our honest condolences to Kato's loved ones, ' he finished.