Authorities in Wenzhou, known as China's Jerusalem, have given Christian churches a deadline to remove prominent crosses within weeks, worshippers and an activist group said Thursday, stepping up a long-running campaign.

The eastern province of Zhejiang, where Wenzhou is located, earlier this year proposed rules requiring crosses for Catholic and Protestant churches to be attached to the front of the building, rather than on the roof. They must also be no more than a tenth of the building's height.

The move came after Wenzhou authorities last year demolished the large Sanjiang Church, following government claims it was an illegal structure.

Three parishes under Wenzhou's jurisdiction told AFP that local officials had renewed demands for churches to remove the remaining crosses themselves, threatening to take them down if they did not comply.

A member of the Yongqiang Parish told AFP: "Talk has been spreading that in the past two days, more than 10 crosses have been torn down in Wenzhou."

Officials had ordered crosses on eight churches to be removed by September 20, he added.

A pastor in Pingyang said that "almost all" of the county's 135 churches had been told to remove crosses.

"Until now, the crosses of small churches in rural areas have been removed. But it will come to the big churches in the end," he added.

The campaign is not restricted to Wenzhou, but with an estimated number of Christians of more than a million, it presents a prominent target.

Bob Fu, president of US-based religious rights group the China Aid Association, said the pace has "definitely increased".

"It seems there is a government directive to finish the campaign under a deadline," he told AFP.

But church members said they had seen no formal documents, and received only verbal orders.

"Now we have people guarding the churches. It's also likely that there will be clashes," said a church representative in Tengqiao town.

The government moves have generated opposition. Photos circulated online showed worshippers making small wooden crosses, painted red, to be displayed as a form of protest. Priests also demonstrated outside the Wenzhou government offices last week, according to Catholic news service UCAN.

An article in the state-backed Global Times newspaper on Wednesday quoted government religious officials as saying crosses had been "relocated" indoors for "the sake of safety and beauty".

The state-linked China Christian Council estimates the country has around 20 million Christians -- excluding Catholics -- in official churches supervised by the authorities.

But the true number of worshippers could be higher, at least 40 million to 60 million, according to some estimates, as some pray at "underground" or "house" churches which seek to exist outside government control.