Two elderly women have been beheaded in front of a crowd of onlookers in Papua New Guinea in the latest of a spate of brutal attacks in the country against people accused of witchcraft.

Police at the scene were outnumbered by an angry mob and were forced to stand by as the women were murdered in a remote village, the Post-Courier newspaper reported.

Bougainville police inspector Herman Birengka said his men had been "helpless".

It is understood the two women had been suspected of causing the death of a local teacher through sorcery.

"The two women were rounded up and taken to Lopele village after they were suspected of practising sorcery and blamed for the death of a former teacher, who was from Lopele village," Mr Birengka said.

The newspaper reported that the two women had been tortured for three days before the murders, suffering knife and axe wounds. Police were sent to the remote village to act as mediators but were held back by the mob, who were reportedly armed with firearms, knives and axes.

The killings come days after six women accused of sorcery were reportedly tortured with hot irons in the country's Southern Highlands and last month a woman was burned to death by a mob, leading Amnesty International to call for more action to prevent violence associated with accusations of witchcraft in the country.

The killings have led 1,000 people to march through the streets of Buka, in Bougainville Province, in protest against sorcery-related killings, Radio Australia reported.

Local human rights leader Helen Makena, chairman of the North Bougainville Human Rights Committee, told Radio Australia that the feeling at the rally was "sadness" but that women and men "spoke out and condemned the barbabaric killing".

Amnesty has urged Papua New Guinea's government to address the violence in the Pacific nation, where many still believe in sorcery.