ONE inmate was killed and 19 injured in an explosion at a notorious Philippine prison where inmates were revealed to be "living like kings" with stripper bars and jacuzzis, and where an eight-year-old girl was recently sexually assaulted.

The explosion happened at 9.45am at a section of the Bilibid national penitentiary in suburban Manila held by a gang known as the "Commando", according to initial reports.

A senior police official suggested a fragmentation grenade could have been used since most injuries came from shrapnels.

At least one inmate was reported killed, but police had yet to release details.

Those injured were taken outside the prison to hospitals.

Investigators who rushed to the scene suggested that the bombing could have been due to a turf war precipitated by a government crackdown on the prison that yielded stashes of drugs, cash and guns, as well as sex dolls, a stripper bar and a jacuzzi.

A network of air-conditioned "villas" was said to have been built for powerful crime lords operating their syndicates from inside the prison.

One investigator said the bombing seems to have targeted the bunkers of the Commando gang, whose leader, J.B. Sebastian, is suspected of having snitched to the authorities.

Sebastian's "villa" was not raided in police raids, even though it housed a large music studio.

The crackdown instead netted Sebastian's rival, Herbert Colangco, leader of the Batang City Jail gang, who has been moved out of the penitentiary.

Colangco made headlines when it was revealed that his "villa" had a recording studio where he cut an album that won a music award.

Earlier in January, public outrage at the way things are run at the prison exploded when it was reported that an eight-year-old girl, who was visiting her inmate father on New Year's Day, was found sprawled on a bathroom floor, naked from the waist down and with a rope tied around her neck.