A Greymouth petrol station worker has been left "very shaken" after a person brandishing a samurai sword held up the store.
Police say the offender entered the BP station at 3:15am on Saturday, carrying a 50cm-long weapon and demanding cash.
The person then escaped on foot, heading on to Tainui Rd.
The offender was wearing dark pants, white shoes and a hoodie or jacket with light-coloured sleeves covered in writing and a black body.
The sword was silver with a black sheath.
Police say nobody was injured in the robbery.
Police conducted a forensic scene examination at the BP this morning and are following up several leads. They want to hear from anyone who saw anything suspicious in the area at the time, or who can help identify the offender.
Anyone with information is asked to call Greymouth police on (03) 768 1600. Information can also be provided anonymously via Crimestoppers on 0800 555 111.