Police were examining CCTV footage from cameras in the area but did not have a description of the attacker.
The stabbing happened in the park, on the increasingly popular Hatea Loop where people walk, run and cycle, between 6pm and 6.45pm.
The victim was wearing a bright-yellow raincoat. He was able to phone for help.
Police would not say how many times the man was stabbed or whether anything was stolen.
However, they said the man had been left "traumatised and confused by the whole experience and very fearful".
It was at least the third major knife crime in Whangarei in just over three days, after a pizza-delivery man and a woman were robbed at knifepoint on Wednesday, but there was no evidence they were linked.
Anyone who may have seen the man, or any suspicious behaviour, in the area around the time of the attack should call Whangarei police on 09 4304500 or 0800 Crimestoppers 0800 555 111.