Colin Prebble, who owns the Subway, said a man entered the store, jumped over the counter, grabbed a staff member and threatened to bash their head in with a rock at about 8.35pm on Sunday.
The man made the employee open up the cash register, from which he took about $270 cash.
Prebble said the employee was "shaking like a leaf".
The employee, who was recently the victim of a home invasion, had stayed calm and been "amazing", Prebble said.
He said the Subway had been robbed a few times over the years, but this is the first time a staff member had been threatened.
It was a "traumatic" experience. "Just horrendous," Prebble said
He said a passerby had seen the robber, followed him and managed to wave down a police car and point out the guy who robbed the store.
"All credit to the guy who just sort of followed him and effectively managed to get him taken into custody."
Raymond Belsey, 24, appeared in the Christchurch District Court charged with the aggravated robbery of the Subway.
He was remanded in custody without plea and is due to appear again in late September.