Quasi-Christian religious group the Church of the Almighty God accused of spreading rumours that world will end on Friday

Chinese authorities have detained 500 people belonging to a quasi-Christian religious group called the Church of the Almighty God for spreading rumours that the world will end on Friday, according to the country's official news agency, Xinhua. Four hundred of the arrests, which have taken place over recent weeks, were in the north-western Qinghai province and the remainder in eight other provinces.

"The Qinghai police bureau stated that the police had stormed numerous centres belonging to the Almighty God cult, arresting more than 400 members and confiscating over 5,000 items including banners, DVDs, slogans, books, computers, speakers, and cell phones," Xinhua reported, adding that the group had "advanced anti-detection capabilities".

The report did not say which government department had orchestrated the arrests. "It's the government – which part of the government, nobody knows," said Zhou Xiaozheng, a sociology professor at Renmin University in Beijing. "The government controls the media, so nobody's allowed to report on it."

Human rights groups say the Chinese authorities maintain a vast network of shadowy, extrajudicial agencies that crack down on dissidents and unauthorised religious groups. The most notorious of them, the 610 Office, was established in 1999 to control the spiritual group Falun Gong. The group was outlawed that year after thousands of followers staged a silent protest outside of the Communist party's central leadership compound in Beijing.

"Though Falun Gong remains the primary focus, its targets now include house church Christians, Buddhists and other religious or spiritual groups," said a 2011 report on the office by the Washington-based Jamestown Foundation thinktank. "Today, based on extrapolating from district-level numbers on local government websites, we estimate it retains at least 15,000 officers."

China's state bureau of religious affairs declined to comment.

Theories that the world will end on 21 December, the last day on the cyclical Mayan calendar, are popular in China. Much of the furore seems to have been inspired by the Hollywood film 2012, a box office hit in China, which used the so-called "Mayan apocalypse" as its central premise.

Chinese media outlets have been told to dampen coverage of the rumoured cataclysm. "Strengthen positive guidance and forcefully guard against the creation and spread of rumours, as well as working up panicked feelings," said a leaked directive posted to the internet by the Berkeley, California-based China Digital Times. The terms Almighty God and Eastern Lightning, another name for the group, have been blocked on the country's most popular microblog, Sina Weibo.

The Almighty God group was founded in the 1990s by self-proclaimed grand priest Zhao Weishan in central Henan province. Among the group's core tenets are the belief that a female Jesus Christ will save adherents from the end of the world and that it must fight a decisive battle against the "Big Red Dragon", its term for the Chinese Communist party. Zhao left China for the US 12 years ago, seeking religious asylum.

"They're saying the Bible is outdated," said a leader of an unofficial church in Beijing who requested anonymity. "They make sure their interpretations are very adapted to Chinese culture, so it's easy for Chinese people to understand what they're preaching."

Hu Xingdou, an economist at Beijing Institute of Technology and well-known commentator on Chinese social issues, said quasi-religious groups were proliferating outside the country's major cities.

"In general you're beginning to see a moral vacuum in Chinese society," he said. "Corruption is terrible, the wealth gap is terrible, everyone just wants to make more money. All of these bad things create the ideal circumstances for the growth of a cult."

Additional research by Chuan Xu