Police are investigating an alleged armed robbery at a Saint Heliers Bay Bar.

About 11pm on Saturday, an hour after the bar closed for the night, a staff member opened the door to put out the rubbish when police say two men forced their way into the building.

The men, who police say were armed with what is described as a black handgun, took a quantity of cash, and fled on foot.

The staff member was not injured in the robbery, and no customers were in the bar.

Police are looking for two men who were wearing balaclavas and dark clothing.

"They are believed to be about 25 years old and were of skinny to medium build.