Eighteen leaders of a major Chinese underground church were formally arrested on Tuesday, a Christian NGO advocate told Reuters, meaning they will eventually face trial and a potential prison sentence of up to three years.

Nearly 30 pastors and staff belonging to Zion Church, an unofficial "house church" not sanctioned by the government, were detained by police nationwide in mid-October, Reuters earlier reported, in the biggest crackdown on Chinese Christians since 2018.

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The group, which includes church founder Pastor Jin Mingri, is being held in detention centres in the southern city of Beihai.

Beihai police could not be reached by telephone for comment. China's ministry of public security did not immediately respond to a faxed request for comment.

Five people were released in October and a further four support staff were released on bail around November 10, Grace Jin, the daughter of Jin Mingri, told Reuters.

The remaining 18 detainees were formally arrested and charged with the crime of "illegally using information networks", said Bob Fu, the founder of Christian NGO ChinaAid, who is in close contact with relatives of the detained pastors and Zion Church leadership.

The crime carries a prison sentence of up to three years.

After a criminal suspect is detained in China, their formal arrest marks the beginning of a criminal investigation leading to trial, a process which could take over a year in complex cases.

Jin, 56, was able to meet his lawyer on October 14, after the case started receiving foreign media attention, Grace Jin said. She previously told Reuters that her family was worried about the health of her father, who requires medication for diabetes, and the detainees' access to lawyers.

U.S. Secretary of State Marco Rubio condemned the detentions and called for the immediate release of the group last month.

The crackdown on Zion Church came a month after new rules from China's top religion regulator banned unauthorised online preaching or religious training by clergy, as well as "foreign collusion".

China has more than 44 million Christians registered with state-sanctioned churches, the majority Protestant, official figures show. But tens of millions more are estimated to be part of illegal "house churches" that operate outside the control of the ruling Communist Party, according to thinktanks and NGOs.

Zion Church, with about 5,000 regular worshippers across nearly 50 cities, rapidly added members during the COVID-19 pandemic through Zoom sermons and small in-person gatherings. The church was founded by Jin, also known as Ezra, in 2007, after he quit as a pastor for the official state-controlled Protestant church.

A graduate of the elite Peking University, Jin converted to Christianity after witnessing the 1989 Tiananmen crackdown, a spokesperson for the church has said.

In 2018, police shut down its church building in Beijing, during a crackdown on major house churches. Earlier this year, police temporarily detained 11 Zion Church pastors, a church spokesperson previously told Reuters. (Reuters, but headline rejigged)

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