'When they released me, they handed me a notification of the criminal detention of my husband,' she said. The notification said Wang had been charged with 'gathering a crowd to disrupt social order'.

'I am rather worried because criminal detention is quite a serious measure,' she said.

Then known as Wang Tongjiang, Wang was involved in the 1989 Tiananmen pro-democracy movement as a student and was imprisoned for a year. He assumed the name Wang Dao after his release.

With the tightening of rules for independent, domestic, non-governmental organisations and a continuing crackdown on human rights lawyers, many fear the survival of the mainland's fledgling civil society is being threatened. The days leading up to the anniversary of the June 4 crackdown also typically see the authorities rounding up dissidents or those they perceive as posing threats to social stability.

Wang's wife said police summoned him on Friday and detained him for five hours. They had summoned him three times during the past three months and had once told him to leave Guangzhou permanently, she said. 'They said it's even better if you leave the country.'

Police also broke up an outdoor service held by Wang's church at a park in Guangzhou on Sunday morning, Wang's wife and another person said. Dozens of people were worshipping in the park when police arrived to take pictures and videos, before ordering worshippers to leave. Two people were taken away by police but released soon afterwards.

The Liangren Church, which has a young following, resorted to worshipping outdoors because the congregation was barred from holding a Sunday service at their regular place of worship on May 2. The church was forced to keep changing its venue because police had repeatedly pressured landlords to evict it over the past few years, Wang's wife said.

In an open letter posted on the internet on May 3, Wang appealed for support from other Christian churches, saying his church had become a target for police investigation after it became actively involved in aid work in the aftermath of the Sichuan earthquake in 2008.

'The room for survival for Chinese house churches is shrinking,' Wang wrote.

Guangzhou police and religious affairs bureau officials refused to comment.

Rights activists say authorities have stepped up the persecution of Christian churches in recent months. In November, the Beijing-based Shouwang Church, with about 700 members, was forced to worship in a park in a snowstorm after being evicted from its rented premises. Later that month, the 1,000-strong Shanghai Wanbang Church was also forced to worship in a park after the authorities declared its activities illegal.

Officially atheist, the ruling Communist Party permits worship only in state-approved churches, although millions of Christians continue to worship in unregistered 'house' churches.

Zhang Lifan , a former academic at the Chinese Academy of Social Sciences, said the central government looked on non-government and religious bodies with suspicion, especially after the 'colour revolutions' in former Soviet states. He said it was an unwise move.

'It is very wrong to see NGOs as a confrontational force ... as most do not want to be a political force,' he said. 'Civil society can act as a buffer amid social conflicts but [now] there is nothing there. Throughout history, social unrest happened when there was no civil society but only underground movements.'