They said he surrendered peacefully and was in good health.

ACT Policing acting superintendent traffic operations and planning Susie Ball said officers would clear the unit to ensure it is safe for other residents to enter the apartment block.

Police had previously ordered residents to evacuate the Monaro Crescent complex after noticing a "strong smell of fuel coming from the apartment". That smell had begun to dissipate by 9pm.

Acting superintendent Ball said the surrender was the best outcome police could have hoped for.

"The person of interest is in custody and he is safe and secure. None of the police involved have been harmed and none of the members of the public have been harmed," she said.

Police established a cordon around the building and closed Monaro Crescent south of La Perouse Street while they negotiated the surrender of a 39-year-old man, who they addressed through a loud speaker.

Police's Specialist Response Group of negotiators, tactical response unit and canine unit were on scene, as were firefighters and ambulance intensive care paramedics.

Acting superintendent Ball said the man in the unit lived there, and he was previously known to police.

He had made no demands and was not considered violent.

Police said they were alerted to the incident by another resident of the unit earlier on Sunday. That resident told police the 39-year-old man had barricaded himself in the unit overnight after an argument, and that he had allegedly assaulted the resident with a weapon. Police would not say what type of weapon was used.

The second resident allegedly received minor injuries in that incident.

"While the offender was distracted, the man managed to flee the apartment and went to City Police Station around 10am. He alerted them to the location of the offender who is still in the unit," police said.

One neighbour from the block of units, who did not want to be named, said he noticed a smell of petrol around the building in the afternoon.

"I thought what the hell is that?" he said.

"I just didn't think twice about it."

Another neighbour, who also didn't want to be identified, heard commotion outside at 4am on Sunday.

"There was a car dropping somebody off," she said.

"There was a lot of noise happening. I thought maybe my laundry was being broken into."

When she went outside she saw the noise came from the unit the man had barricaded himself in.

Police, who arrived at the scene about 3.30pm and ordered the evacuation a short time later, taped off pathways near the units and the Red Hill shops.