Police were carrying out a scene examination and making further inquiries into the robbery.
The staff member who was threatened was being given support, he said.
This comes as the Herald today reported police intelligence documents revealed aggravated robberies of shops had more than doubled in the past two years, with cigarettes being targeted by thieves almost 500 times in a little over a year - quadrupling previous estimates.
Offenders wielding guns, knives and hammers in search of "gold bars" of tobacco have left shopkeepers "constantly living in fear" and resorting to fighting back with their own weapons.
A previously unreleased police intelligence report from September last year found there were at least 490 burglaries and robberies in which cigarettes were targeted in a 13 month period - more than one a day, and more than four times the estimate the Herald made after analysing media reports of burglaries.