The owner of a pit bull beaten to death with a cricket bat while it fought with another animal says her family is devastated by the "preventable" loss.

ACT Police are assisting the ACT Government in an investigation into the incident, which was caught on CCTV.

According to Vanessa De Alvia, the owner of the dog, Karma, which was killed, the drama began on Thursday when her two dogs ran out of her north Canberra home as her children greeted a neighbour.

"She came over, had the little pug behind her, and the kids had opened the door and the dogs had got out the front door," she said.

"They just started playing tug-of-war with the pug.

"The kids had separated the dogs apart from it. All they had to do is grab the other dog by the collar … and put the dogs in the house."

GRAPHIC CONTENT WARNING: Footage may be confronting.

Sorry, this video has expired WARNING GRAPHIC FOOTAGE: Man beats fighting dogs with cricket bat

The man, who did not own any of the dogs involved, then intervened with a cricket bat, repeatedly striking the two larger dogs with force, in an apparent attempt to break up the fight.

After both dogs released the pug, he continued to swing the bat.

One of the beaten animals was killed.

Ms De Alvia, whose children were watching on during the incident, said she did not recognise the man, and was unsure whether he lived in the area.

"There was a hose that was right next to them that they could have used," she said.

"He could have grabbed the collar. He could have tried several other ways before using the cricket bat."

She said her 12-year-old son had been an emotional mess since the incident.

"He's not doing well," she said.

"[Karma] had never been violent … she just want to cuddle all the time and slept with me every night.

"This was totally unnecessary."

Neighbour Jenifer Hanson who witnessed the incident said she was yelling at the man to stop.

"It felt like it went for about 12 minutes but it would have happened in a minute," Ms Hanson said.

"It still doesn't feel real."

Police were called following the incident, and a spokesman for ACT Policing said officers were helping the ACT Government's Domestic Animal Services in its investigation.

'Darned if you don't and darned if you do'

Ms De Alvia's other dog Pumbaa the Staffordshire bull terrier was also involved in the incident. ( Supplied )

Canberra dog trainer Bruno Grutzner said the issue of whether dog owners and bystanders should intervene in a fight was controversial.

"You're going to be darned if you don't and darned if you do," he said.

"If you do not interfere your animals are going to get hurt … and if you do interfere you are most likely to be injured as well."

Mr Grutzner said in some circumstances startling dogs would stop them fighting.

"If you do decide to go in there, you've got to go in hard," he said.

"There is the possibility for these dogs to get out of this frame of mind and take note of what has just happened and possibly get a fright."

But he said bystanders who did not know the fighting dogs should be particularly wary of getting involved.

"I would always say caution first, safety first, don't interfere," he said.

"As a newcomer it's highly likely that these two dogs will turn towards you."

Limited legal rights for bystanders

Criminal lawyer Paul Edmonds said minimal force should be used if a person interferes in a dog fight.

"If you are in a public park and another dog attacks your dog ... you are legally entitled to use all reasonable and necessary force to get that dog off your dog, if that prevents that dog from attacking a person," he said.

"If it is a life-threatening situation for your dog, an owner may be required to use lethal force against the other dog."

But Mr Edmonds said the law would only give very limited protection to a bystander.

"Unless that bystander has some legal right in relation to either animal involved," he said.

"The safest thing would be to stay out of that incident."