The Civic building was shut down on Tuesday afternoon the alarm was raised over the hazardous material scare.

Level nine of Eclipse House on London Circuit in the city was shut down for over 90 minutes after 1pm as police and a fire and rescue team attended the scene.

ACT electoral commissioner Phil Green said people opening postal votes on the ninth floor discovered the material inside several envelopes.

People working on the floor were sectioned off from where the material was discovered while the building was placed into lockdown. People outside the building were not allowed back in.

Meanwhile vote counting continued unencumbered on the fifth floor.

Mr Green said police and emergency crews were able to determine the substance was not hazardous and the building was reopened after about an hour and a half.

He said police had taken it away for analysis but it was not a white powder.

"This is the first time we've had anything happen like this for some years," he said.

"A long time ago when white powder was the big thing we had a couple of envelopes turn up with it but it turned out to be dried paint.

"We don't take chances and we had to lock the building down."

ACT Policing later confirmed that routine precautions had been taken after dirt came into the building with a postal vote.

The building was reopened shortly after 3pm.

More than 240,000 votes had been counted through the centre as of 4pm on Tuesday.