A Gonville resident rang emergency services when she heard a commotion at about 4pm on Sunday.
"I was here having a cigarette and started hearing the yelling," she said.
She came out on to the footpath and saw a man kicking another man in the head.
"He lost the plot big time," the witness said. "He just kept yelling 'I'm going to f***ing kill you' - he was determined he was going to kill him."
There were about three or four others around, a lot of swearing, before the man was eventually dragged up a driveway, the resident said.
"All I saw was that one person kicking him."
Another person appeared to be holding the attacker back, she said.
"He wasn't kicking him, he was booting him. There's no way you can survive something like that - a 57-year-old man wouldn't have had a s*** show against people like that. He must've been pretty beaten."
Yesterday a section of Rimu St was cordoned off and was being guarded by security personnel.
Detective Senior Sergeant Neil Forlong said: "There is a team of a dozen staff working on the homicide inquiry, which is in its very early stages.
"The team is trying to establish exactly what has happened in the hours leading up to the assault and what have been the factors that have contributed to this."
Wanganui District Council Gonville representative Jack Bullock said his thoughts were with the whanau of the man.
"In the short time I have known this man, I really believe he wanted good change for what he was involved in," he said.
Another district councillor, Philippa Baker-Hogan, said she understood the attack was gang-related and called for an increased police presence.
"Council and the community need a strong level of assurance from New Zealand Police that extra policing resources will be immediately released to Wanganui in the aftermath of this violent gang-related death," she said.
Sources informed the Chronicle that the attack involved members of Black Power. A post-mortem is expected to be conducted today.
Police are not looking for anyone else in relation to the assault but have appealed to the public for information on any disorder in the Rimu St area on Sunday. Those who have information can contact Whanganui police or provide information anonymously through Crimestoppers on 0800 555 111.
