China Monday appointed a new chief for its top police and judicial body, which tackles crime and security issues such as subversion, political dissent and social unrest.

Police minister Meng Jianzhu has replaced Zhou Yongkang as head of the ruling Communist Party's Politics and Law Commission, Xinhua news agency said in a short dispatch.

The move follows last week's party congress which saw President Hu Jintao stepping down from his top party post to make way for Xi Jinping.

Zhou had been set to retire following two five-year terms in the post and Meng had long been seen as his successor.

But the move has resulted in a downgrading of the commission. Zhou ran it as one of nine members of the party's Politburo Standing Committee, the top decision-making body, while Meng is a mere member of the 25-member Politburo.

The Communist Party, which has ruled for more than 60 years, controls all aspects of the state and government.

The Politics and Law Commission is in charge of the police force, internal security system and the judiciary. It oversees a "stability maintenance" budget that amounted this year to $111 billion, more than the nation's declared defence spending.

Besides greatly empowering the police during his leadership of the commission, Zhou also oversaw crackdowns on political dissent as well as on ethnic separatism in the far-west Xinjiang region and in Tibet.

Social unrest has also risen markedly in recent years, with an estimated 180,000 protests in 2011 over a wide range of issues including corruption, government land grabs, police brutality and social welfare.