Towering eight stories over wheat fields, the Golden Lamp Church was built to serve nearly 50,000 worshippers in the gritty heart of China’s coal country. But that was before hundreds of police and hired thugs descended on the mega-church, smashing doors and windows, seizing Bibles and sending dozens of worshippers to hospitals with serious injuries.

Today, the church’s co-pastors are in jail. The gates to the church complex in the northern province of Shanxi are locked and a police armored personnel vehicle sits outside.

The closure of what may be China’s first mega-church is the most visible sign that the communist government is determined to rein in the rapid spread of Christianity, with a crackdown in recent months that church leaders call the harshest in years.

Authorities describe the actions against churches as stemming from land disputes, but the congregations under attack are among the most successful in China’s growing “house church” movement, which rejects the state-controlled church in favor of liturgical independence and a more passionate, evangelical outlook.

While the Chinese constitution guarantees freedom of religion, Christians are required to worship in churches run by state-controlled organizations: The Three-Self Patriotic Movement for Protestants and the Chinese Patriotic Catholic Association for Roman Catholics.

But more and more Chinese are opting to choose their own churches, despite them being technically illegal and subject to police harassment. Christians worshipping in China’s independent churches are believed to number upwards of 60 million, compared to about 20 million who worship in the state church, according to numbers provided by scholars and church activists.

House churches have been around for decades, but their growth has accelerated in recent decades, producing larger and larger congregations that are far more conspicuous than the small groups of friends and neighbors that used to worship in private homes, giving the movement its name.

Their expansion and growing influence has deeply unsettled China’s rulers, always suspicious of any independent social group that could challenge communist authority. Fears that Tibetan Buddhism and Islam promote separatism among Tibetans and Uighurs also drive restrictions on those religions.

“They are so afraid of rallying points developing for gathering of elements of civil society,” said Daniel Bays, who follows Chinese Christianity at Calvin College, a religious school in Grand Rapids, Michigan.

While house churches have faced varying degrees of repression depending on the region and political climate, the latest crackdown appears to specifically target the largest congregations.

At least two other large churches have recently faced similar crackdowns.