"He is currently in a serious but stable condition in hospital," she said.
A St John spokeswoman said the man had been flown to Waikato Hospital in a critical condition yesterday.
Details including whether the victim was known to his attacker, the circumstances surrounding the incident or the weapon used were not available.
Hay said there did not appear to be any risk to members of the public.
"We would also like to reassure the community that even though this happened in a public place, we do not believe there is any risk to the wider public."
She is asking witnesses to the assault, or anyone who saw a black Great Wall ute in the Taneatua or Ruatoki area on Sunday afternoon to contact them.
* Anyone with information is asked to contact police via 105 and quote file number 200621/9344. Alternatively, contact Crimestoppers anonymously on 0800 555 111.