The Zion church in Beijing, one of the city's largest unofficial Protestant 'house' churches, has operated with relative freedom for years, hosting hundreds of worshippers every weekend in an expansive, specially renovated hall in north Beijing.

But in April, city authorities asked the church to install 24 closed-circuit television (CCTV) cameras in the building for 'security', Zion's head pastor, Jin Mingri, told Reuters.

'They wanted to put cameras in the sanctuary where we worship. The church decided this was not appropriate,' Jin said over tea in his spacious, book-lined office. 'Our services are a sacred time.'

When the request was refused, police and state security agents started harassing churchgoers, calling them, visiting them, contacting their workplace and asking them to promise not to go to church, according to statements from the church and interviews with congregants.

China's constitution guarantees religious freedom, but since President Xi Jinping took office in 2012, Beijing has tightened restrictions on religions seen as a challenge to the authority of the ruling Communist Party.

China's religious affairs bureau and the public security ministry did not respond to faxed requests for comment.

The Chinese government says greater oversight of religious activities is needed in order to regulate believers and facilitate worship, as well as to prevent foreign forces from influencing China's internal affairs using the guise of religion.

House or official

China's Christian believers are split between those who attend unofficial 'house' or 'underground' churches and those who attend government-sanctioned places of worship.

The unofficial establishments, which range from small living room-gatherings to large, professional operations like Zion, had in recent decades been tolerated by authorities.

They were often able to rent large spaces, though these are rarely identifiable from the outside.

In February, new legislation increased oversight of religious education and practice, with harsher punishment for practices not sanctioned by the authorities.

In addition to being asked to install security cameras, some unofficial churches have been asked by police to take detailed lists of attenders' IDs and phone numbers, churchgoers and activists say.

Some who push back have been visited by police and asked to switch places of worship to officially sanctioned churches, they added.

The Zion church, which occupies an office building floor that was previously a nightclub, is now being evicted despite previous verbal assurances from its landlord that it could rent the location until 2023, Jin said. The landlord could not be reached for comment.

Jin does not expect to be able to find a landlord that would rent the church another suitable location.

Rare protest

There are roughly 60 million Christians in China, most of them Protestant, with about 10 million Catholics, according to independent estimates.

The Vatican and Beijing are locked in talks to resolve a decades-long dispute over appointing bishops in China that, if resolved, could make underground Catholic churches official, with Holy See-approved bishops

On July 23, more than 30 of Beijing's hundreds of underground Protestant churches took the rare step of releasing a joint statement complaining of 'unceasing interference' and the 'assault and obstruction' of regular activities of believers since the new regulations came into effect, according to a copy of the statement seen by Reuters and confirmed by Jin.

'We call on the government to respect history and the current situation of house churches, respect the means and practices of religious work, and respect citizens' basic freedoms and rights to believe,' the letter said.

Wang Yu, a prominent rights lawyer who has defended Christians from harassment and was recently baptised at Zion after years of worship there, said she believes the pressure on believers is an attempt to force the church to close.

'The authorities hope numbers will dwindle till it becomes impossible to continue, but in recent months ever more churchgoers have been attending services,' she said.

Wang fears, however, the situation will worsen, given the authorities have started describing the church as a 'cult' when pressuring churchgoers. In one of its statements, Zion also says authorities have called the church a cult.

'Being labelled a cult was how it all started for the Falun Gong in 1999,' Wang said, referring to the spiritual movement the Communist Party banned that year.

The new regulations have increased government pressure on the churches to 'sinicize' – to be culturally Chinese and submit to oversight from the Communist Party – but many have resisted, saying this would be a fundamental betrayal of their faith.

'House churches believe that our spiritual needs and the content of our faith is ruled over by God,' Pastor Jin said.

'What we need is the freedom to believe. Without this, it is not real faith.'