The men took money from the till and escaped in a silver Subaru Legacy that was later found abandoned in Exminster St.
It had been stolen from Greenpark Rd, Penrose, a few days before.
The robbery had some similarities to two others in Mt Eden recently and police were trying to establish if there were any links, Ms Williams said.
In those incidents, heavily disguised men threatened shop attendants with a pistol, and in one case forced staff at a liquor store into the chiller.
Ms Williams said the threats made to the Countdown staff were worrying and the police wanted to find the robbers before there was any escalation in violence.
* Anyone who witnessed the robbery or the later dumping of the Subaru, or who knows the identity of any of the robbers, should contact Detective Victoria Williams on (09) 820-5760 or phone Crimestoppers anonymously on 0800-555- 111.