Mark Thorn estimated about 15 young people were involved in the incident in his street about 8pm on Saturday.
His partner called the police, but it took about 40 minutes for them to arrive.
"It could have had the potential to go pear-shaped," Mr Thorn said about the incident.
At least two people had baseball bats, attacking others before taking off.
Others were wielding wheel braces.
If someone had died, there would have been "hell to pay".
"Our concern is the delay was unacceptable on a Saturday night in Oamaru. Saturday nights are busy and police should not be under-staffed," he said.
"They are the community's front line and responsible for providing coverage."
While waiting for police, Mr Thorn and a friend tried to calm things down.
Mr Thorn estimated two police officers arrived in a patrol car about 40 minutes after the call was made about 8pm.
Other police arrived after that.
An ambulance arrived within 10 minutes of being called by someone else, because of concerns there could be injuries after one person was hit across the shoulder blades with a baseball bat and another had a hand injury, he saidPolice estimated the ages of the two groups ranged from mid-teens to early 20s and the altercations moved between several streets, arising from a dispute between individuals in each group.
Acting officer in charge of the Waitaki police district, Detective Sergeant Mike Ryder said the situation on Saturday night was "not ideal", as the response "took a long time".
Police received a number of phone calls about the incident.
Some of the Oamaru staff were in Christchurch helping with earthquake relief, while others had been called to a homicide investigation in Roxburgh.
Three police officers were on duty in Oamaru at the time of the incident, but two were attending a serious family violence incident and the third was dealing with a prisoner at the police station.
Police at the family violence incident could not leave until the situation had stabilised and in the other case the officer had to monitor the prisoner.
Det Sgt Ryder said off-duty staff were called out from their homes to deal with the fighting incident; they had to get equipped and get a car before going to the incident.
"I would like to think it [the response] was the exception rather than the rule. Sometimes things happen and we don't have the staff. We just have to prioritise," he said.
He could not guarantee it would not happen again, but it was "highly unlikely".
Det Sgt Ryder said he would be happy to meet Mr Thorne to discuss his concerns.
