The offender grabbed a few banknotes and fled south on Waterfront Dr. The shopkeeper and members of the public gave chase but lost him around a corner.
Four Square owner Harpreet Singh said he was grateful to members of the public who tried to stop the robber.
One woman was unloading her shopping in the trolley bay next to the store entrance when she heard a commotion inside.
She saw a man running out the door with the shopkeeper in hot pursuit so pushed her trolley in front of him, hitting him in theknee.
He panicked and ran off down the waterfront, apparently forgetting his three accomplices waiting in a getaway car in the loading zone immediately outside the shop.
Mr Singh said his brother, Raju, chased the offender down the road but lost him when the getaway car picked him up. It was a red Nissan Maxima.
"We'd like to thank the woman with the trolley, and also members of the public who tried to chase him," Mr Singh said.
Mr Murdock said it appeared to be an opportunist crime with no weapon or threats involved.
The amount taken would be known once store takings were tallied up.
Police were examining CCTV footage.
The alleged offender was described as a male Maori aged 25-30 of solid build and about 6 feet (183cm) tall.
He was wearing a black woollen hat, blue pants and a cream jacket over a black hoodie.
* Call Mangonui police on (09) 406 2060 if you saw the man fleeing from the town's Four Square or if you know who he is.
