The UN's rights body has expressed deep concern over the case of a young mother burned alive in PNG by a crowd that accused her of sorcery.

On Wednesday, Kepari Leniata, 20, was reportedly stripped naked, tortured with a branding iron and tied up, splashed with fuel and set alight on a pile of rubbish topped with car tyres, while a crowd that included school children looked on.

According to news reports, she was burnt in Mount Hagen by villagers who claimed she killed a six-year-old boy through sorcery, with police outnumbered by onlookers and unable to intervene.

"We note with great concern that this case adds to the growing pattern of vigilante attacks and killings of persons accused of sorcery in Papua New Guinea," said Cecile Pouilly, a spokeswoman for the UN Office of the High Commissioner for Human Rights.

"We urge the government to put an end to these crimes and to bring perpetrators of attacks and killings to justice through thorough, prompt and impartial investigations in accordance with international law."

The UN agency also asked that authorities "demonstrate their political will" by educating the public to prevent more attacks and by providing protection to people accused of sorcery.

"In light of the heinous crime which has been committed, we encourage the authorities to hasten the process to strengthen the legal response to such killings," Ms Pouilly said.

The agency also said authorities should "provide medical and psychosocial treatment for victims".

There is widespread belief in sorcery in the poverty-stricken Pacific nation where many people do not accept natural causes as an explanation for misfortune, illness, accidents and death.

There have been several other cases of witchcraft and cannibalism in PNG in recent years.

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

AFP