Papua New Guinea police have arrested four men over last week's deadly ambush on an Australian trekking group, while villagers killed a man for allegedly harbouring the attackers.

Seven Australians, a New Zealander and their porters were attacked while trekking along the Black Cat Track in Morobe province on Tuesday.

Two local porters were killed and seven more were admitted to the Angau hospital in Lae, all with deep gashes to their legs.

On Sunday police arrested four of the six men wanted in connection with the vicious attack.

Police commissioner Tom Kalunga says three men were captured at Wau at one end of the Black Cat Track and the other was arrested at the other end at Salamaua.

The ABC understands the four suspects have been locked up at the police station in the provincial capital Lae.

Officers are still hunting for the remaining two suspects and Mr Kalunga says it is only a matter of time before they are brought in.

Suspect killed in revenge attack

Matthew Gibob was one of the porters who died in the attack and on Saturday his relatives killed a man they believed was linked to the ambush.

The dead man's body is in the morgue in Wau with large machete wounds to his back and head.

The family of murdered porter Kerry Rarovu mourn his death near Wau. ( ABC: Liam Fox )

Ninga Yawa, the chairman of the Black Cat Trail Association, says Mr Gibob's relatives attacked the man and he died on the way to hospital.

"They felt that he deserves to be treated the same way as they treated Matthew," he said.

Mr Yawa believes people from Bitoi, an alternate but largely unused start to the Black Cat Track, are responsible for last Tuesday's attack.

Commissioner Kalunga says no-one has the right to take another life and the killing will be investigated.

The family of the other slain porter, Kerry Rarovu, have covered their faces in mud - the traditional mark of grieving.

They are demanding answers and justice.

"My family feel that the criminals must die the same as Kerry died," his brother Bing Rarovu said.

'Frenzied bloody massacre'

Meanwhile, the leader of the trekking group, Christy King, has spoken to the ABC about what she says was a "frenzied bloody massacre".

"I am deeply saddened and would like to offer the families of the two porters who lost their lives on Tuesday afternoon during the attack at Banis Donki my sincere condolences," she said.

"The attack was a frenzied bloody massacre which made no sense. I am so sorry for these men to have received such terrible injuries."

Black Cat Track trek leader Christy King.

Due to the severity of their injuries, the porters were forced to remain on the track overnight following the attack while Ms King and the trekkers were escorted by local police to safety.

Since the attack, just one of the porters has undergone surgery to clean his wounds, prompting Ms King and her husband Daniel to set up bank accounts for donations towards their treatment.

At this stage it is doubtful any of them will be able to walk properly again.

"I'm worried about my future. Maybe I'll stay alone, I don't know. I'm going to be paralysed maybe, I don't know," one of the porters told the ABC.

Former local trekking operator Tim Vincent says the motive behind the the attack is still not clear.

"[There are] only rumours and half stories at the moment. Everyone is talking about these ex-criminals and escapees, possibly they were involved," he said.