Armed police had been negotiating with at least one person inside a building on the Canturf site on Cessnock Street until the operation ended about 2pm.

Officers blocked off streets in Fyshwick from about 11am.

Details of the incident remain scant, but journalists and workers in nearby areas were told to keep back and out of line of sight for safety.

Following the incident, ACT Policing station sergeant Rod Anderson said no one had been injured and officers had made no arrests.

Police have found an item and begun investigations, but would not say what happened at the building nor how many people were involved, except to confirm most divisions of the police force had been called to the operation.

"We had things under control, we had police resources in place and at no time was any member of the community put in any danger," Sergeant Anderson said.

ACT Policing was called to the Canturf site about 11am after receiving reports of suspicious activity and a possible firearm.

They did not know if the person or people were armed. Several police vans and an ambulance were at the site.

A police drone was used at 11.30am. At 12.30pm, two tactical police vans approached the property and armoured police exited. Police began negotiating using a loudspeaker at 12.45pm.

The Artemis Early Learning Centre was in lock down as part of the operation.

Workers near the Goolwa Place-Cessnock Street intersection were allowed to stay but police stopped people from accessing Cessnock Street.

A woman said she was walking down to collect a removalist truck down the road about 11.30am when she saw at least four police officers "in full flak gear" watching the Canturf building from behind their cars.

Another person who worked in the area first noticed police cars arriving about 11am, and was told by police to stay inside.