Shearing Sports NZ spokesman Doug Laing said the wool handler was rushed to hospital after collapsing at the event.
An on-site medic had attended Nooroa on the stage.
Laing said Nooroa grew up in Masterton and had been a competitor almost from the time wool handling was formally added to the programme in 1985.
He won the junior wool handling title in 1988 before becoming Golden Shears open wool handling champion in 1992.
In that 1992 final the runner-up was eventual multiple World and Golden Shears champion Joanne Kumeroa.
Nooroa had finished competing in the final of this year's veterans wool handling event, for competitors aged over 60, when he collapsed on the stage, Laing said.
"The programme [came] to an abrupt end as an on-site medic and others, including a trained nurse, worked frantically on the veteran. A defibrillator was also on-hand in the Masterton War Memorial Stadium, where the Golden Shears have been held every March since the event was established in 1961."
Golden Shears president Phil Morrison said everyone was hoping for a speedy and full recovery.
"We are thinking of Mii and the family and friends, and wishing them all the best.
"The whole shearing industry and sport, around the World, is one big family. Obviously everyone is feeling for the well-being of Mii Nooroa."