A woman is believed to have been held at gunpoint as a man robbed a store in Nelson last night.
The man, who was wearing a balaclava, entered the Brook St Store around 7.15pm and demanded the assistant open the cash drawer.
He threatened to harm her if she did not co-operate, police said.
"The offender was carrying an item under a scarf which had the appearance of a pistol barrel. He took a sum of cash from the till before leaving without further incident," Detective Sergeant Ian Langridge said.
The man was believed to have fled the scene on foot.
The shop assistant was left "shocked and shaken" by the incident, he said.
The man was wearing a black knitted balaclava, black track pants and a plain black polar fleece jacket with a zip down the front.
He was described as white, possibly middle aged, of slim build with brown eyes and red cheeks.
Anyone who witnessed the incident, or who may have seen a man fitting the description, is asked to contact Mr Langridge on 03 546 3840, or anonymously contact Crimestoppers on 0800 555 111.