Police were not yet releasing the description of the robber, only to say he was a man.
Mr Membery said the robber left the bar, which was formerly known as the DB Tavern, through the garden bar area and ran towards the Murray Linton Rose Gardens on the corner of Ward and Trigg Aves.
A reporter at the scene earlier this evening said police, including a police dog, appeared to be searching the surrounding streets.
She said staff members and police were inside the bar.
Meanwhile, Mr Membery said Rotorua CIB were now at the scene.
He said the staff member who was held up was recovering from the ordeal.
"He is understandably shaken up by the event but he was not injured during the incident."
Mr Membery said any members of the public who had information about what happened should contact the Rotorua police immediately on 0800 CRIMESTOPPERS.
He said the robbery was not connected to an incident that happened shortly afterwards at Countdown in Central Mall where a teenager allegedly pulled a steak knife on staff who approached him for shoplifting.
Mr Membery said the teenager allegedly ran outside the supermarket and kicked the side of a car that had a woman inside.
With help from members of the public, the teenager was found at a nearby house and was being dealt with by the Rotorua police's Youth Aid Section, Mr Membery said.