Papua New Guinea police have arrested members of an alleged cannibal cult accused of killing at least seven people, eating their brains raw and making soup from their penises, a report said Friday.

The 29 people, who appeared in court this week charged with murder and cannibalism, were part of a 1,000-strong group formed to combat errant sorcerers who The National newspaper said had begun charging exorbitant fees.

The cost of a witch doctor revealing a cause of death or casting out an evil spirit was usually 1,000 kina ($475) cash, plus a pig and a bag of rice, but some were also demanding sex as payment.

"It's against our traditional ethics and morals for a sorcerer to have intercourse with a man's wife or teenage daughter," said one local cult leader in the Tangi area, inland from Madang province on PNG's northeast coast.

"That was the main cause of frustration that led to the forming of a group to hunt down sorcerers.

"Over time, as suspects were released to carry on as sorcerers, we got tired and fed up."

There is a widespread belief in sorcery in the impoverished Pacific nation where many people do not accept natural causes as an explanation for misfortune, illness, accidents or death.

In 1971, the country introduced a Sorcery Act to criminalise the practice. But PNG's law reform commission recently proposed to repeal it after a rise in attacks on people thought to practice black magic.

Locals determined to get revenge on the profiteering witch doctors sought their own supernatural training from village chiefs, using their "possessed" bush knives to hunt down and kill seven people since April, the report said.

"We ate their brains raw and took body parts such as livers, hearts, penis and others back to the hausman (traditional men's houses) for our chief trainers to create other powers for the members to use," one of those arrested said.

The killings saw police raid Biamb village last week and arrest 29 people, eight of them women. Their case in the Madang district court was adjourned until August 17 so police could collect more information.

A local expert in the supernatural cited by the newspaper said the group operated differently to traditional PNG hausman practice, where specific people are typically trained to hunt a sanguma (sorcerer).

"But these people never kill sorcerers in broad daylight, mutilate and eat sorcerers' flesh, livers, and hearts or make soup from the penis of sorcerers," he said.

"This is insane and the cannibalism (of this group) goes beyond the local culture."

Madang provincial police commander Anthony Wagambie urged other followers of the group, believed to number more than 1,000, to surrender.

"It is the tip of the iceberg and more needs to be done to educate locals to eradicate the movement," he told The National.

"Police cannot do it alone. It requires collective effort from government, responsible agencies, non-governmental organisations and the churches to work together."

There have been several other cases of witchcraft and cannibalism in PNG in recent years, with a man last year found reportedly eating his screaming, newborn son during a sorcery initiation ceremony.

In 2009, a young woman was stripped naked, gagged and burnt alive at the stake in the Highlands town of Mount Hagen in what was said to be a sorcery-related crime.