Police said as the two workers approached the man, he then threatened them with the firearm. He was last seen walking down Church Street towards Summerhays Street.
Detective Sergeant Dave Thompson said the bar employee was distressed by the incident but had done everything right.
"We're very fortunate that nobody was hurt. I'd like to acknowledge the bar employee, who did everything right in what must have been a very distressing and stressful situation. She followed instructions and took note of important details."
He said the man would have returned home with money, mainly in $1 or $2 coins.
"This is sure to attract the attention of family, friends or associates, so we're also appealing to them to get in touch with us.
"Any offence of this nature is disturbing. There were a number of patrons in the bar at the time of the robbery, along with the employees."
The man has been described as European, 6 foot, of thin to medium build and possibly aged in his late 20s or early 30s. He is believed to have thick black or dark brown shoulder length hair and a receding hairline. He was wearing a long-sleeve brown shirt, blue jeans and possibly a paintball mask.
Police also believe the offender may have removed his shirt walking down Church Street. They would like to hear from anyone who may have noticed a man of this description in the Church Street/Summerhays Street area on Saturday afternoon.
Anyone with information which may help identify the offender is asked to contact Detective Steve Field on 06 213-9652. Information can also be provided anonymously via Crimestoppers on 0800 555 111.
