Four people have been arrested after a string of aggravated robberies over a two hour period in south Auckland overnight.

Detective Sergeant Tom Gollan said it was of great concern that the offenders were willing to use violence to obtain "petty" amounts of money and property.

The first incident happened outside Everglade Liquor Store in Manukau about 10pm.

Two teenagers armed with a BB gun allegedly tried to rob the store but were confronted by two workers outside.

There was a scuffle and one of the workers was hit several times over the head with the gun before the offenders fled empty-handed, police said.

The same offenders then allegedly demanded cash and cigarettes from two men on Cavendish Drive, about 5km from the Liquor store, and pointed the BB gun at them when they did not comply.

The victims managed to run away and contact police, who arrested two teenagers, aged 16 and 18, a short time later.

Then on Station Rd in Otahuhu, two men in a car allegedly demanded cash from people coming out of a party. When they refused to hand over anything the offenders pulled out firearm - believed to have been an imitation - and took off with a small amount of money.

Police arrested the alleged offenders a short time later.

The Takanini Burger King was later robbed by a man who approached the drive through window on foot and allegedly threatened the worker with a knife and stole the till.

He was yet to be found but police were following positive lines of inquiry, Mr Gollan said."Obviously it's greatly concerning when you've got people presenting weapons and threatening people for such insignificant amounts of money and property. It is a worry."

The four arrested will appear in Manukau District Court tomorrow.