Pedestrians had to leap aside and a store owner thought a motorbike being ridden on the footpath in Victoria Ave was going to smash through his shop.
The incident in central Whanganui happened early this afternoon.
A pedestrian, who did not want to be named, said he was in the Victoria Ave block between Guyton and Ingestre streets when he saw the dirt bike on the footpath and had to jump out of the way.
"He was coming right at me," he said.
"He was ****ing moving, I can tell you that. It's lucky the footpath was pretty empty."
Ross Fallen, who was walking down Guyton St, said he had to dive into a building to avoid being hit.
"I heard the sound of the motor behind me and realised he was on the footpath," Fallen said.
"I know that as chairman of Mainstreet, I'm not popular with some people but I didn't think anyone disliked me that much. I'm just a volunteer."
The bike travelled from Guyton St along the footpath on Victoria Ave before it hit some advertising signs and a pillar near the Ingestre St corner and the rider fell off.
Bin Inn Whanganui owner Sammy Singh said the bike had earlier been past his shop on the Victoria Ave/Ingestre St corner several times and was "very loud and very speedy".
"When I heard it on the footpath, I thought it was going to come in here through my front window," Singh said.
"The tyre slipped on the footpath and the bike hit the post outside. He flew off the bike. It's lucky the shopping trolleys were outside our shop. They saved me.
"He's very lucky there was no-one on the footpath and that he's still walking. It's not worth it."
Whanganui Police Sergeant Colin Wright said the incident followed issues reported by the public.
"We had a lot of members of the public ringing about a bike charging around Guyton St and Victoria Ave and down to Trafalgar Square," Wright said.
"We had officers trying to locate it and they saw it near the Victoria Ave/Guyton St corner. The rider then came up on to the footpath and lost control further along Victoria Ave and slid into a pillar."
Wright said an 18-year-old man had been checked by St John staff and had no serious injuries.
"He was just winded."
The Police Serious Crash Unit had been advised.