When we reached Sanjiang, in Zhejiang province, an elderly woman was angrily telling the pastor how at the end of April police dispersed members of her congregation and neighbouring ones who had come to protect their new Protestant church from being bulldozed. Several pastors were arrested and many detained, including those from the Sanjiang church – one of the officially sanctioned (and government controlled) "patriotic" churches. Many supporters were also arrested, including pastors from the underground house church movement. One, who asked to be referred to only as W, escaped the police raid by hiding in a nearby warehouse.

For years, during her evening walks, the woman had watched the construction work taking place on the massive church, which was just a few hundred metres along the main road from her house. When we were there in May, flashing lights warned us of the police roadblock that had closed off access to the church weeks ago, after the Chinese government ordered it to be pulled down. "They want to remove every trace," said W. The old woman added: "During the Cultural Revolution they burned Bibles, but they didn't remove the crosses." The old church survived the Cultural Revolution, but in such a dilapidated state that it was converted into a mat-weaving factory.

The town of Sanjiang lies on a flat strip of land opposite the city of Wenzhou, where the Ou river broadens before pouring its mass of grey water into the South China Sea, 350km south of Shanghai. The township has been earmarked for a new business district alongside the market gardens, so the local government encouraged a plan for a church worthy of its entrepreneurial ambitions. About 15% of Wenzhou prefecture's 9 million inhabitants are Christian.

Wenzhou has a history of its inhabitants migrating to Europe in the last century. It has been neglected by the Chinese government in recent years. Nevertheless, since the economic reforms, the city has been celebrated as the Chinese capital of private enterprise and Christianity, a mutually advantageous relationship that has given rise to it becoming known as China's "Jerusalem". In the urban sprawl between sea, river and mountain, red crosses dot the skyline, marking – mostly Protestant – places of worship. The city boasts 1,500 churches in every possible architectural form, from elongated white buildings bearing the Chinese character that means love to squat grey brick ones to massive edifices in fake freestone with domes and colonnades.

Cao Nanlai, a Chinese anthropologist, published a book, Constructing China's Jerusalem, about the town's particular social dynamics, with its Christian bosses devoted to both conquering new markets and converting their workers.

The budget for the church in Sanjiang was close to $5m. After nine years of dealing with bureaucracy, raising funds and building work, the massive structure rose from the ground with a 60-metre high tower, a 30-metre long transept and a 50-metre long nave bordered by pilasters and arches. It resembled a European gothic cathedral. An annexe served as a home for the elderly. The cross was mounted on 8 August 2013.

In early 2014, church demolitions were reported in several towns in Zhejiang province, Shanghai's rich hinterland. Many crosses deemed too obtrusive were forcibly taken down. Early in April, a Catholic church in a rural county of Wenzhou was demolished and the cross on a Protestant church destroyed. A dozen other churches received ultimatums to pull down buildings or crosses in a campaign against "illegal structures", launched in Zhejiang in 2013. However, Christians in Wenzhou observed that the campaign only targeted churches.

Orders were obeyed in some places, but Sanjiang resisted. "We knew that even if we removed the cross it wouldn't stop there, and therefore we had to stand firm," said W. Although the surface area of the building had exceeded the authorised size, the Sanjiang church administration was confident because its "model church" had received local government approval. "Finally, a compromise was reached when the authorities agreed only to knock down the top two floors of the annexe. But they didn't keep their word," said one evangelical minister from Wenzhou, who asked to be referred to as "Peace".

Chinese security officials monitor a religious parade at a Catholic cathedral in Donglu, Hebei Province. Photograph: Mark Ralston/Getty

On 26 April, 1,000 people, many from neighbouring congregations, came to pray in front of the church in the hope of preventing its destruction. The following day, some 40 church leaders identified as having influence on their congregations were arrested, including official cadres and members of the house church movement. Pastor Peace spent 20 hours in police custody. The riot police intervened at 4am on 28 April, and by 8.30pm the massive church was reduced to rubble.

A pastor in Beijing who monitors the persecution of Christians said: "By making a clean sweep of Sanjiang, the government wants to set an example and show that nothing will stop it." Six other churches or their adjoining buildings were earmarked for demolition in Wenzhou in May. One Protestant church was converted into a "cultural auditorium". In the weeks that followed, the crosses on 15 churches in the Wenzhou region were destroyed and removed by crane.

According to the American NGO China Aid, since the beginning of the year 60 churches in Zhejiang province have received notice that either their crosses or their buildings must be demolished – more than 40 of these are in China's "Jerusalem".

Christians in Wenzhou have not seen such sustained persecution since the Cultural Revolution. According to pastor Joy, a member of the same evangelical network as pastor Peace: "The local government and the churches have always got along well here." Only the heads of the free churches dare to speak out – anonymously of course – because they know that their churches are under threat. The "official" pastors have been forbidden to speak out. The fear now is that the government will turn its attention to the house churches.

China's government-approved churches, such as the one in Sanjiang, have not been targeted in this way before. The officially authorised Protestant Three-Self Patriotic Movement, and the Chinese Catholic Patriotic Association, are organised in such a way as to cloister Chinese Christians from foreign influence. This necessarily gives rise to compromises. For instance, the Three-Self Patriotic Movement encompasses all Protestant denominations in a single doctrine.

Chinese believers have always been able to adapt, and some frequent the official churches as well as the free ones. The clergy also compromise – for example, there are "official" bishops who obtain secret benedictions from the Vatican. In fact, the patriotic churches, be they Catholic or Protestant, have been encouraged by the government to absorb the Christian explosion in China as much as possible. In addition to the official 24 million Protestants and 6 million Catholics, there are reportedly tens of millions of "clandestine Christians" in the country today.

In Sanjiang, people weren't blaming the Wenzhou authorities. They believe that the orders came from Xia Baolong, the Communist party chief and former governor of Zhejiang province. "It comes from much higher up, Wenzhou is just a testing ground for a widespread offensive against Christian influence," said one pastor, citing internal sources. Xia was Xi Jinping's deputy from 2003 to 2007, before the latter became the country's president.

Xi, a leading promoter of China's economic renaissance, incarnates an unashamed patriotism in which neo-Maoism and neo-Confucianism coexist – so long as they contribute to assuring the Communist party's supremacy and promoting its sacred heritage. "The number of Christians has grown to such an extent that there are now more Christians in China than party members and that scares them," said pastor Joy. "But Christians still have a negative image in China where there is a history of persecution. All that has played a part."

For the Beijing pastor, this anti-Christian campaign is part of a stated objective by the new leadership to promote Chinese cultural traditions such as Confucianism and Buddhism. It is no coincidence that much media attention was devoted to Xi's visit to Confucius's birthplace in February. On that occasion, according to the Chinese news agency Xinhua, Xi called for the propagation of a nationwide "ethical doctrine" with "fundamental socialist values" based on "traditional Chinese culture". According to pastor Joy, among themselves party members often use the pejorative expression yang jiao to designate Christianity. It translates as "foreign teaching".

This article appeared in Guardian Weekly, which incorporates material from Le Monde