Ottio, who was an ever-present in the World Cup as the Kumuls won their group before losing to England in the quarter-finals, was signed by the Betfred Super League club from Canberra as a replacement for Corey Thompson.
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.
"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."
Widnes Vikings are shocked and saddened to learn of the passing of Kato Ottio: https://t.co/q4aMtjBTk0 #RIPKato 🇵🇬 pic.twitter.com/iBwoeFx7ko
— Widnes Vikings (@WidnesRL) 8 January 2018
He added: "Having only learned this morning that Kato had developed a sudden health issue whilst training yesterday, 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."
WATCH: See our new man in action, PNG's #RLWC2017 star, Kato Ottio: https://t.co/MvB8ERoV66
— Widnes Vikings (@WidnesRL) 1 December 2017
The "try-scoring freak", “possessing a lethal combination of size and speed", will be ripping it up for the Vikings in 2018. âš«ï¸âšªï¸ pic.twitter.com/7bFteyykIs
Widnes head coach Denis Betts, who is also assistant England coach, said: "To receive this tragic news is heart-breaking
"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."
Thanks to everyone from #PNG for their great comments following the signing of Kato Ottio! Keep up to date with his time at the Vikings by following us on Twitter. Widnes Vikings are also on Instagram & Facebook. Proud to have your backing! 🇵🇬⚫ï¸âšªï¸ pic.twitter.com/Hp7jBsyWmh
— Widnes Vikings (@WidnesRL) 3 December 2017
Huddersfield centre Jordan Turner, who played with Ottio in Australia, said on his Instagram account: "Devastated to hear the news of kato's passing, some very fond memories with him from my time in Canberra.
"Legend of a bloke. Will be truly missed and was a Superleague star in the making. My thoughts go out to his family. RIP Brother."
