Authorities in China's Guangdong province have intensified their monitoring of Christian communities, forcing church closures in some places.
Officials are targeting unofficial "house" churches not regulated by the ruling Chinese Communist Party (CCP), Radio Free Asia said.
"A lot of churches are getting these letters saying they are carrying out illegal religious activities now, and requiring them to stop ... Some have been forced to stop gathering for worship, while others have been forced to move premises," pastor Li Peng told the RFA.
The clampdown follows an extended campaign by religious affairs officials in Zhejiang province, where crosses on church buildings were torn own.
Christians in the region say their attempts to legally challenge the move failed.
Believers in other provinces like Guangzhou and Shenzhen have also complained about recent crackdown on churches with specific focus on crosses that the authorities say are illegal structures.
"A lot of churches in Guangzhou are being persecuted, including the Guangfu church run by Ma Zhao and others. Churches in Shenzhen have also been targeted, but not to the same degree," said Zhang Mingxuan, president of the Chinese House Church Alliance.
A protestant believer in Shantou's Chenghai district was arrested as she was handing out leaflets to people as part of a conversion campaign.
China's state-run Global Times denied in July authorities demolished crosses on churches, but admitted some crosses had been "relocated" out of safety concerns, a Reuters report had said.
More than 1,500 churches had their crosses demolished or removed in Zhejiang province, ChinaAid, a Texas-based Christian advocacy group, said last year.
China officially grants freedom of religion, but religious activities are allowed under the strict watch of the Communist party and the state machinery.