A patron at Caroline's Celtic said the local man had been thrown out of the bar for fighting, and he had helped pull him away from trying to hit another man. However, he didn't think the man he was trying to fight was the same person who eventually grabbed a chainsaw.
The next thing he had heard was the man calling for his friends to come and back him up outside, and a chainsaw starting up.
When he got outside to look, people were coming from all directions to stop the man with the chainsaw, and he was in the middle of the road between the Celtic and Supercheap Auto.
He didn't see who hit the chainsaw wielder, but did see that man lying on the road. He thought the man may have had a broken jaw because he was moaning and unable to speak properly.
The man was moved to the side of the road and put into the back of a van to await an ambulance, he said.
Caroline's Celtic bar manager Caroline Norton said she had spoken to staff and a man had been removed from the bar for "bad behaviour" but there had been no fight.
The man and his friends had left and got into an altercation with another group of people across the street in front of the service station, across from Supercheap Auto, she said.
Someone had heard a chainsaw start and one of her staff members had called police.
Since it happened some distance from them, they weren't sure what was going on.
Ms Norton said she and her staff did their best to ensure people were safe and enjoyed themselves and she was disturbed by something like that happening.
Staff at businesses surrounding the area that were open at the time were unable to comment yesterday.
No charges have been laid and the matter is still under investigation. The unknown assailant has yet to be identified.
Police are interested in hearing from witnesses who saw the incident. Anyone who did is asked to call Whanganui police on 3490600 or provide information anonymously through Crimestoppers 0800 555 111.