Hundreds of people were evacuated from Canberra's tallest building for about two hours after signs of smoke were seen in its basement.

Emergency services allowed staff to return to the building about 10.30am, although they were unable to find the cause of the smoke. 

They were called to Lovett Tower in Phillip, just next to the Woden Plaza, about 8.40am on Tuesday morning.

They evacuated up to 600 people from the building as a precaution.

Lovett Tower is one of the few ACT buildings over 20 floors.

Emergency services had found no sign of fire at 10.30am, when they allowed staff to return to the building.

They ventilated the basement area and were expected to leave the area a short time later.

Two pumpers, a command vehicle, a breathing apparatus truck, the Bronto Skylift Hydraulic Platform and a hazardous materials unit are on scene.