A US-based group, the Cardinal Kung Foundation, which monitors allegations of religious oppression in China, said Bishop An Shuxin was freed this week.

The Chinese Church was established in the 1950s, after Beijing and the Vatican broke off diplomatic relations.

It is believed to have several million followers, but the BBC Dan Griffiths in Beijing says it is thought that millions more belong to the underground Church.

Religion has flourished in China since economic reforms began more than 30 years ago, our correspondent says, but the government still exerts tight control over all religious activity in China, fearing any challenge to its authority.

In the past, many other followers of the underground Catholic Church have also received lengthy prison sentences.

And many Buddhist monks and nuns have been jailed for their loyalty to the exiled Tibetan spiritual leader, the Dalai Lama.

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