Residents of Papua New Guinea's Porgera region say they're fearful a "new brand of tribal warfare" has started after gunmen stormed a passenger bus, killing at least seven people.

Local police told the ABC that 10 people armed with guns and machetes set up a roadblock and ambushed the bus on Tuesday night as it was travelling on a highway near the Porgera mine in Enga Province, a region in the country's north-east.

WARNING: This story contains images and descriptions some people may find distressing.

Video of the incident spreading on social media, seen and verified by the ABC, shows a number of dead bodies on the passenger bus, with broken windows and glass shattered over the seats. 

In another video, local residents are trying to assist people injured from the incident, pulling bodies out of the bus through the windows.

Enga Provincial Police Commander, Chief Superintendent Fred Yakasa told the ABC seven people died in the attack. He said between 10 and 13 others were seriously injured and were being treated in hospital.

"Police are trying to establish the facts and the motives [behind this attack]," Superintendent Yakasa said. 

"Our priority is to secure public safety."

Authorities are advising residents in the area to avoid using public buses, known locally as PMVs, due to safety concerns. 

Police believe the ambush is linked to the death of a man at the centre of illegal mining accusations earlier this year.

The province has been at the centre of ongoing tribal violence, with police in September announcing the state of emergency for the region after at least 30 people were killed in continued violence between rival clans. 

Most of the violence stems back to illegal mining in the area, with the valley home to one of Papua New Guinea's largest gold deposits.

However PNG police spokesperson Mark Karambi told the ABC's Pacific Beat Program the bus killings took place outside of the designated state of emergency declared area in the region.

He said early investigations indicated it involved different tribes from the groups at the centre of the violence in August and September.

"The police are currently present in Porgera and around that area, but this is an incident that happened when police kind of moved," he said. 

"Police were there for about some good hours, but they left to attend to another incident when that happened."

Mr Karambi said the driver of the bus was one of the seven killed. He said a passenger took control of the bus after the driver was killed, steering it away from the gunmen and to the local hospital so those injured could be treated. 

A Porgera resident who spoke to the ABC after learning of the killings said people in the area were "terrified" that this kind of attack meant a "new brand of tribal warfare" had started.

"[Now] any innocent person travelling is just murdered as pay back," he said. 

"The government needs to send more security personnel into Enga Province. 

"Surunki [where the incident took place] is under Lagaim District [and] the current state of emergency is only being declared in Porgera Paiela district. 

"[The government] needs to declare the state of emergency for Lagaim District so we can have security forces in both districts as they are importantly the corridors into Porgera and out of Porgera."

United Nations humanitarian advisor Mate Bagossy said there were no wider humanitarian consequences of the attack for the time being, but the UN was monitoring for possible spillover.

"We are also concerned about access to people in need in Mulitaka and Porgera valley," he said.

The attack took place on the only road into Mulitaka, where a large landslide claimed around 160 lives in late May.

Humanitarian organisations have continued to provide support in the area, but efforts have been complicated by tribal conflicts.

The ABC has contacted the Papua New Guinea government for comment.