Hong Kong's Cardinal Joseph Zen has urged the release of Cui Tai, an underground church bishop reportedly abducted by Chinese authorities in April.

In a Facebook post on Tuesday, Cardinal Joseph Zen, a Chinese Catholic cardinal, said the government must release Mgr Augustine Cui Tai and 'put an end to the inhumane and illegal detention', according to the Hong Kong Free Press.

Cui Tai, a bishop of Xuanhua in north China's Hebei province, reportedly faced repeated persecution for refusing to accept the authority of the Chinese Patriotic Catholic Association, the official denomination run by the atheist state. He went missing in mid-April, believed taken by government officials, and has not been seen since.

Cui Tai is part of China's underground church, and as a bishop is recognised by Rome.

According to the Justice & Peace Commission of the Hong Kong Catholic Diocese, Cui had attracted opposition since 1993 due to church gatherings deemed illegal and 'unlawful missionary work'.

The commission said the bishop has faced particular oppression since 2007, according to Asia News. He underwent 'almost non-stop' house arrest, which involved being detained in detention centres, hotels or forced to travel with a government escort. The group strongly condemned the 'Chinese government's violation of fundamental human rights and religious freedom'. It warned that the bishop's health has deteriorated in recent years and urged that the state guarantee his health and safety, and demanded his imminent release.