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.
"We are interested in speaking with the customer who gave him the cigarette and anyone else who was in the store or in the area around that time," Mr Wainhouse said.
"No one else is believed to be involved in the robbery."
Anyone with information can contact Detective Constable Karl Reyland of Whanganui Police on 349 0600 or Crimestoppers anonymously on 0800 555 111.
There have been at least 14 aggravated robberies in Whanganui since December 2016, with cigarettes, cash and alcohol being the most common targets.