In recent weeks, hundreds of members of the Almighty God group have clashed with police, sometimes outside government buildings, in central Henan, northern Shaanxi and southwestern Gansu provinces, according to photos on popular microblogs.
The government says it is a cult calling for a "decisive battle" to slay the "Red Dragon" Communist Party, and which has been spreading doomsday alerts related an old Mayan calendar seen by some as predicting "the end of the world" on December 21.
Police have now detained around 1,000 members the Almighty God group across some seven provinces, the People's Daily reported on its website on Thursday, saying about 400 of them had been detained in the remote western province of Qinghai.
The sect's followers have been distributing leaflets saying that the world will end in 2012, state media have said.
China's Communist Party brooks no challenge to its rule and is obsessed with social stability.
It has taken particular aim at cults, which have multiplied across the country in recent years. Demonstrations have been put down with force and some sect leaders executed.
Former President Jiang Zemin launched a campaign in 1999 to crush the Falun Gong religious group, banning it as an "evil cult" after thousands of practitioners staged a surprise but peaceful sit-in outside the leadership compound in Beijing to demand official recognition of their movement.