Two Oamaru males, aged 17 and 18, were arrested and charged with aggravated robbery.
Although Detective Warren Duncan said police were not seeking anyone else, he would like to speak to two young women who were outside the dairy at the time, and who spoke to the victim after the robbery.
"They may have seen the offender after the robbery, so we are very keen for them to approach us, so we can have a chat."
Police were told a man wearing a balaclava and holding a knife entered the Thames St shop at 3pm on Saturday, before threatening a lone 22-year-old woman and taking cigarettes.
Det Duncan said the man then ran off before escaping in a car.
Items linked to the robbery had now been recovered, but police were still keen to hear from any other witnesses, he said.
"We did a search warrant yesterday and found the car, found the offenders, found the knife and the balaclava.
"It's got the potential to have a far worse outcome, especially when you start pulling a knife on someone. In the heat of the moment things can happen, of course.
"Luckily, in this instance no-one was hurt, but I think it is fair to say the victim in the matter is quite shaken up."
