China has executed a man who held six women as sex slaves in an underground prison and killed two of them, state news agency Xinhua said, in a crime which shocked the nation.

Li Hao, 36, was convicted of murder and rape in Luoyang Intermediate People's Court in the central province of Henan in 2012, Xinhua said.

State media reported in 2011 that the former local government employee kidnapped six nightclub and karaoke bar workers and repeatedly raped them in a self-built dungeon. Two of the six were found dead when a 23-year-old woman escaped and led police to the basement.

Li forced them all into prostitution and filmed them in pornographic videos he put on the internet, Xinhua said. He then instructed three women to kill two of the other captives.

The three women were found guilty of murder but were given lenient sentences. One was jailed for three years and two were put on probation, Xinhua said.

"According to details revealed by the police, Li's motive was to make money by forcing the women into prostitution or to appear in obscene webcasts," the report added.

Li was executed "according to law" after meeting close relatives in the jail, Xinhua said.

After the case became public, Luoyang's police chief apologised for failing to act sooner and suspended four police officers, it added.