"The pressure on grassroots organisations has never been this intense," said Zhang Zhiru, who runs a labour rights group in the southern manufacturing city of Shenzhen in Guangdong province. In the past year, his car has been vandalised, and police harassment has forced his organisation to move more than 10 times. In December, the last of his five employees quit. Regulations that took effect last month in Guangzhou, capital of Guangdong province, have intensified scrutiny of non-profit organisations that receive foreign donations, and the central government has proposed legislation to tighten controls on foreign non-government organisations active in China, according to the state-run Xinhua news agency. With Chinese philanthropists wary of upsetting the authorities, funding to Mr Zhang's organisation, the Shenzhen Chunfeng Labour Dispute Service Centre, has dried up, and even Chinese crowdfunding websites refuse to list it. "The government just wants us to disappear," Mr Zhang said. The campaign has focused on groups deemed sanctuaries for dissent. From its cramped offices in the university district of north-west Beijing, the Transition Institute championed a mix of free market economics and support for the downtrodden, conducting research on the exploitation of taxi drivers, school policies that short-change rural children and the environmental costs of the massive Three Gorges Dam on the Yangtze River. But the institute also attracted advocates of democratic reform, some of whom had prior run-ins with the authorities. "We always hoped to eke out survival in tough circumstances," said Mr Yang, 43, the researcher now in hiding, who spent eight years in prison for holding informal discussions with a group of friends about multi-party elections and a free press. "But the more independent NGOs," he added, referring to non-governmental organisations, "especially the ones that criticise government policies or don't help the government's image, have encountered a policy of containment, even destruction".

Before its employees began vanishing, the Transition Institute was part of an undergrowth of privately funded organisations that spread despite the government's ambivalence toward independent, civil society groups. Guo Yushan, an activist and economist from rural eastern China, established the think tank in 2007 after parting ways with a legal rights advocate, Xu Zhiyong, who embraced a bolder approach to campaigning for citizens' rights. "You can make your arguments online, or write articles criticising the government, but once you mobilise people you're going to have some serious problems," Mr Guo said in an interview shortly after Mr Xu was arrested in the summer of 2013 for organising street protests against official corruption. Mr Guo's new think tank avoided street activism. Instead, it aimed to give citizens the expertise and arguments to win a bigger say in government policy, a process that Mr Guo argued would help China move peacefully toward democracy. He and his team of researchers picked subjects that brought into focus questions about the reach of the state - such as tax policy - and then spread their findings through meetings, reports and media interviews. The authorities closely monitored the institute's work, especially the lectures and conferences it organised. "Sometimes they would force us to limit the number of attendees, and sometimes they would just tell us to cancel an event at the last minute," Mr Yang said.

The Communist Party says charities and other grassroots organisations can offer much-needed social services in a nation strained by poverty and urbanisation, and the number of such organisations has grown. But the party is also wary of citizen activism that it cannot control, and groups must be sponsored by a state entity before registering as non-profits. Like many others, the Transition Institute instead registered as a private business. The furtive relationship that many Chinese grassroots organisations have with the government makes it difficult to count just how many there are, said Anthony Spires, an associate professor at the Chinese University of Hong Kong who studies China's non-government organisations. He estimated there were between 2500 and 3000, excluding those that are essentially puppets run by the government. "They help fill a need in Chinese society that the government recognises," he said. But that tolerance, he added, "can be taken away at a moment's notice". The Transition Institute was especially vulnerable, partly because a large share of its annual budget of $US480,000 to $US650,000 has come from overseas foundations, according to former employees, who would not specify the sources, fearing it might hurt other groups that receive donations from abroad. Such foreign links are viewed with suspicion by the party authorities who increasingly consider international foundations to be agents of political subversion. The institute's troubles mounted in 2012, after Mr Guo helped the blind legal advocate Chen Guangcheng escape from house arrest in rural Shandong province. Mr Chen later found refuge in the US embassy in Beijing, prompting a diplomatic crisis and a deluge of international news media attention. Not long after Mr Chen departed for the United States, the police put Mr Guo under house arrest for 81 days.

The institute resumed its research, but whenever it convened a meeting or event, the police visited and issued warnings. In July 2013, officials from the civil affairs department, which oversees non-government organisations, raided the institute's offices, seized hundreds of copies of research reports and accused the institute of operating illegally. Early last year, Mr Guo resigned as head of the Transition Institute. His wife, Pan Haixia, said he told her that security officials had promised in exchange to allow the institute to register as a non-profit and continue its research, provided it refrained from organising meetings or other events that could become a magnet for protests. But in early October, the police detained a former intern, Ling Lisha, for photocopying leaflets supporting the pro-democracy protests in Hong Kong and discovered that she had asked the copy shop for a receipt under the name of the institute. Days later, just before 2am on October 9, more than a dozen police officers and security agents rushed Mr Guo's apartment on the outskirts of the capital. They grabbed personal computers, an iPad and mobile phones, and led Mr Guo away. The police also raided the institute's offices three times that month, taking away more material each time an employee was detained. Calls and faxed requests for comment to the Beijing Public Security Bureau went unanswered.

With his colleagues disappearing one by one, Mr Yang decided to go underground. He was in the institute office one morning in late November when a police officer called and told him to go to a station for questioning. Instead, Mr Yang left an internet message for his wife, shut off his cellphone, and slipped away, taking only the clothes on his back. "It was a spur-of-the-moment decision," he said in an interview. Meeting a reporter at a location several hours' drive from Beijing, he said he missed his wife and four-year-old son, and visibly nervous, he talked about his fear of being returned to prison. Mr Yang said he would turn himself in should a warrant be issued for his arrest, but he was not interested in co-operating with what he described as an extra-legal persecution of his colleagues. "I still don't understand what we did wrong," he said. "We were just trying to help improve China." New York Times