More than 20 people have been killed in similar incidents in the past two months, leaving both the Indian authorities and Facebook-owned WhatsApp scrambling to find a solution in its biggest market.

Police said nine people have been arrested and more are being sought after they found the middle-aged woman's mutilated body near a forest area in the Singrauli district of the central Indian state of Madhya Pradesh on Sunday.

The accused men told police they caught hold of the woman late Saturday after finding her moving suspiciously and seeing a flurry of WhatsApp messages about gangs of child kidnappers in the area, local police chief Riyaz Iqbal told AFP.

"We are trying to identify the victim and have circulated her picture to all the police stations," Singrauli police chief Riyaz Iqbal told AFP.

Last Thursday the Indian government threatened WhatsApp with legal action, saying the "medium" for spreading malicious rumours "cannot evade responsibility and accountability".

WhatsApp said the next day it would test limiting the ability of its more than 225 million Indian users to forward messages and remove the "quick forward button" next to media messages.

It had already announced new features to help users identify messages that have been forwarded and bought full-page adverts in Indian newspapers with tips on how to spot misinformation.

It has however stopped short of acceding to Indian government demands to enable the authorities to trace messages, saying its service would stay "end-to-end encrypted".

Lynchings are nothing new in India, but the spread of smartphones to even the most remote corners has enabled rumours to be shared at lightning speed and in huge volumes.

The spate of attacks related to rumours of child kidnapping started last May in the eastern state of Jharkhand with the emergence of a video that has since spread across India.

People have also been lynched by Hindu extremists murdering Muslims and thrashing low-caste Dalits accused of killing cows or eating beef.