A Philippine politician ordered soldiers, police and other gunmen to kill at least 57 defenceless people in a horrifying slaughter that saw women shot in the genitals, the government alleges.

In the most detailed account yet of Monday's election-linked massacre, which has sent shockwaves through the South-East Asian nation, an emotional Justice Secretary Agnes Devanadera said female victims may have also been raped.

"It was horrible. I cannot begin to describe it," Ms Devanadera told the GMA television network, recounting what she had seen of the bodies as well as the testimony of many of those who had taken part in the killings.

Ms Devanadera said the witnesses told prosecutors that local mayor Andal Ampatuan Jnr ordered his private militia of more than 100 gunmen to open fire on the group of people on a remote farming area in the southern Philippines.

The gunmen had a short time earlier abducted a convoy of aides and relatives of a rival Muslim politician, Esmael Mangudadatu, plus a batch of local journalists.

The group had been travelling to an election office so Mr Mangudadatu's wife could nominate him to run against Ampatuan Jnr for the post of Maguindanao province governor in next year's elections.

Fifty-seven bodies have since been recovered from shallow graves in the killing fields close to a town bearing the Ampatuan name.

At least 22 of the victims were women, police said.

Twenty-seven victims were journalists and 15 were motorists who were driving past the area at the wrong time, all of whom were apparently killed to eliminate witnesses.

Ampatuan Jnr, who surrendered to authorities on Thursday and was taken to Manila where he was expected to be charged with mass murder, has denied any involvement and blamed Muslim rebels for the killings.

Authorities had already said that hundreds of policemen believed loyal to Ampatuan's powerful clan in Maguindanao province had been detained and suspected of being directly involved or linked to the massacre.

Ampatuan Jnr is the son of Maguindanao's governor, a Muslim clan chief of the same name who until this week was a close ally of President Gloria Arroyo's ruling coalition.

- AFP