The victim was assaulted and sustained serious injuries during the robbery, police said.
It was reported that a tall man with a slight build was seen leaving the area in a white vehicle, which drove off toward the (Southern) motorway at speed, the statement said.
Otago police are appealing for anyone in the area who might have seen something to contact police on 105, quoting file number 220303/9442.
Information can also be provided anonymously via Crime Stoppers on 0800 555 111.
This morning, police tape and two police cars remained at the scene when the ODT arrived about 9am.
The open sign remained on in the shop, as did the light above the front door.
Last night, officers interviewed onlookers who formed a crowd at the Mini Mart as police and St John attended, the neighbour spoken to by the ODT said.
People were in the store at the time of the robbery, he said.
The alleged robber was briefly chased down adjacent Bruce St before he got into a waiting Subaru, he said.
Another neighbour expressed shock when she heard about the incident.
''That's so... sad,'' she said.