An influential Protestant church in China says prominent leaders have been arrested in what appears to be a growing crackdown on the underground church movement.

Nine people were detained on Tuesday after police raided their homes and the church office in Chengdu, in central China, the Early Rain Covenant Church said. Five had been released by Wednesday.

More than 1,000 miles away in Wenzhou, authorities began demolishing the Yayang Church building, video obtained by non-profit ChinaAid, which monitors religious persecution, shows.

This latest wave of arrests, after others last year, shows the Communist Party's resolve to snuff out churches that do not align with its ideology, Christian groups say.

The BBC has contacted China's embassy in the UK for comment. Authorities have not made any statements about the arrests or the demolition in Wenzhou.

China promotes atheism and controls religion. The government said in 2018 that there were 44 million Christians in the country, but it's unclear if that number includes those who attend the many underground churches.

The Communist Party has long pressured Christians to join only state-sanctioned churches led by government-approved pastors. But Christian groups say the grip has tightened noticeably, with arrests becoming more common and prompt.

At least two church leaders in China have told the BBC that authorities are swiftly arresting unauthorized church leaders. In the past, these individuals would first be warned, then fined and finally detained if they still refused to comply with orders.

Just weeks ago, Li Yingqiang, the current leader of Early Rain Covenant Church, had said he 'sensed a storm gathering' and referred to 'the imminent prospect of... another large-scale crackdown'.

Mr. Li and his wife, Zhang Xinyue, are among the four who remain in detention. Their church described the arrests as a 'concerted operation' but said the grounds for arrest, and whether those detained had been charged, remain unclear.

In Wenzhou, local authorities brought in bulldozers, cranes, and heavy machinery earlier this week to start taking down part of the Yayang Church building. ChinaAid reported that hundreds of armed and special police officers have been deployed to stand guard outside the building.

This surge in enforcement against independent church networks shows the central government is determined to stamp out Christian churches entirely unless the church is indoctrinated into the party's ideology, said Bob Fu, founder of ChinaAid.

Last year, authorities banned clergy of all religions from preaching live on social media, organizing online activities for children, and raising funds online, unless these were carried out on government-approved platforms.