About 9.45am, police responded to reports of an incident at Garema Place, in a back alleyway alongside King O'Malleys pub in the city.

ACT Policing's head of crime, Detective Superintendent Scott Moller, said the victim had collapsed shortly after being involved in an altercation with another man.

"We are currently working through CCTV footage and all available evidence to piece together all the circumstances surrounding this man's death today," Supt Moller said.

"I'd also like to acknowledge that the man who died today was Indigenous and from ACT Policing's perspective we'd like to express our sympathies to the Indigenous community."

The entrance to the alleyway was cordoned off, with screens put in place to shield the crime scene. The crime scene was expected to be in place most of the weekend.

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It was also suspected the offender involved may have disposed of critical evidence, possibly the murder weapon, as he fled the scene.

On Saturday afternoon, four teams of SES volunteers were called in as crime investigators sought to comb the immediate area, including looking in garbage bins and garden beds to search for evidence.

"We are looking for any available evidence which would contribute to our investigation ... anything and everything," Supt Moller said.

Supt Moller would not disclose whether the victim was a resident of a flat above the crime scene, or visiting the area.

However, the pedestrian-only location was an emotionally-charged area for much of the morning as people, some of whom who clearly knew the victim, came and went.

Police would not disclose how the man currently in custody was identified and apprehended. However, they admitted a foot pursuit did take place. Witnesses reported seeing a man tackled to the ground a block away and led away in handcuffs.

As is customary during a murder investigation, the man held at the ACT Watch House will be subjected to forensic procedures seeking fibre, hair and blood samples. His clothing will also be examined and tested in the AFP laboratories at Majura.

No charges have yet been laid in the case.

For a violent murder to occur in such a busy area of the city, on a Saturday morning, is highly unusual.

"There's a multitude of witnesses but if there's anyone out there who haven't yet spoken with police, I'd ask them to come forward or contact Crime Stoppers on 1800 333 000," Supt Moller said.

Supt Moller was not prepared to release the detail of the type of wounds the victim suffered.

"I want to assure the public that we don't have any concerns for public safety at this stage. We have one male person in custody and we are working through this investigation," he said.

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