A female shop worker received minor injuries to her hand in an aggravated robbery of the Abbot Street Dairy in the Gonville shopping centre.
Whanganui Police Senior Sergeant Shayne Wainhouse said the robbery happened about 7.30am on Sunday, March 25.
"A male entered the dairy to purchase cigarettes," Mr Wainhouse said.
"He spoke to a customer and asked them for a cigarette, which the customer provided, then left the store. We don't believe they were known to each other. The male re-entered the store a short time later, armed with a hammer, and robbed it of cigarettes."
A 23-year-old man handed himself in a few hours later at the Whanganui Police Station and appeared in Whanganui District Court on Monday charged with aggravated robbery.