He then spent about eight minutes walking around the Grandview Shopping Centre in Nawton before going inside, Hill said.
The man was wearing dark skinny jeans, a hooded jacket, baseball cap and white sneakers and is spotted on CCTV peering inside the bar. He then walks inside, through the crowd, approaches the bar and places the gun on the counter.
The man then pulls up a purple-coloured bandanna over the bottom of his face and threatened the two staff.
After handing over the large amount of cash the man has fled, leaving the two frightened staff members uninjured inside.
"It's 7.20pm, it's a busy mall, there's a lot of foot traffic in the area and were a number of patrons inside the bar. It was quite brazen, quite ballsy to go in there when it's so busy," Hill said.
It's unclear what direction the man went from Durham St after leaving the pub.
Anyone who recognised the man in the CCTV images or seen him around the area on Saturday night is urged to contact Hamilton police on 07 858 6200.
Information can also be left anonymously on the Crimestoppers line 0800 555 111.