The persecution of Christians in China appeared to have "entered into a new phase" with the arrest early this week of at least nine Christians protesting the state's ongoing campaign to remove crosses in churches.

Bob Fu, a US-based Christian activist, said the arrest and detention of the Christian activists in the city of Wenzhou in China's Zhejiang province could only mean a heightening of the campaign to persecute Christians in China.

"At least nine people I know have been taken away by the police and that figure is still rising," a provincial church leader told the Guardian. "We think it is a campaign targeting church leaders across the province. It can only be a coordinated action initiated by the provincial government."

One of those arrested was human rights lawyer Zhang Kai, who provides legal support to a number of churches in China, the source who requested anonymity revealed.

Zhang, the Globe and Mail reported, could not be contacted for almost two days after being arrested in the province where local authorities have imposed a deadline for the removal of crosses from church roofs.

The Communist party and the Christian churches in Zhejiang have been at odds since 2013 when authorities started a campaign to demolish so-called illegal buildings.

To date, more than 1,200 crosses have been removed while several churches have been completely demolished, including the Sanjian mega-church in Wenzhou.

Protests have been held against the demolition campaign, which was described by a Catholic leader as an "evil act."

Last Tuesday, plainclothes officers arrested the local Christians. One pastor said he heard from a police official that the "people who were taken away would be put under residential surveillance."

"We are all very angry. They didn't inform people what charges they were being held on and they didn't produce any documents. There are people outside my house. I know if I go out, they might arrest me, too," the source said.

The Radio Free Asia reported that the demolition campaign is part of a three-year urbanisation and beautification project. It seeks to demolish all illegal structures in the province by the end of the year.

Churches are also being audited, with pastors being detained on suspicion of embezzlement after they opposed the removal of the crosses.