"As Dwight's promoter and friend it's unbearable to accept the tragic news that's just surfaced."
One of the country's brightest boxing talents, Ritchie last fought Tim Tszyu, the son of former world champion boxer Kostya Tszyu, in August for the IBF Australasian super welterweight title in Sydney.
He lost by unanimous decision but was to return to the ring next month for a light-middleweight fight against Tommy Browne.
Sydney's Daily Telegraph newspaper reported that Aboriginal Australian Ritchie, who had a record of 19 wins and two defeats, collapsed when sparring with another boxer in Melbourne on Saturday and could not be revived.
Ritchie leaves three children behind.
His death sparked a flood of tributes from local boxers on social media.
"Today we lost one of our own," Australian professional and Olympian Luke Jackson wrote on Twitter.
"I remember having my professional debut on Dwight’s card. Sending my love to his family, loved ones and the whole of boxing Australia."
(Reporting by Ian Ransom; Editing by Daniel Wallis)