The website of one of the mainland's most high-profile liberal research institutions, the Unirule Institute of Economics, has been shut down amid signs that the policing of online dissent is intensifying.
The apparent crackdown comes as the authorities deal with the fallout from the ousting of former Chongqing party chief Bo Xilai and the escape of blind legal activist Chen Guangcheng from house arrest.
Yao Zhongqiu, vice-chairman of Unirule's academic committee, said it was noticed late on Saturday that the website was down, on the eve of the three-day May Day holiday from Sunday.
Yao said: 'We're shocked because we didn't receive any warnings and have not been given any reasons. And nor do we know how long it will remain closed.'
Unirule, founded by economist Mao Yushi (pictured) and a number of liberal academics in July 1993, has been vocal in opposing one-party rule on the mainland. Mao warned on Wednesday that the economy was headed for a hard landing unless the authorities pushed for political reform and freedom of speech.
Several popular microblogs operated by academics and journalists have also been shut down recently. Professor He Bing of China University of Political Science and Law and journalists Yang Haipeng and Shen Yachuan are among those affected.
Professor He was not available for comment yesterday but Wang Xiaodong, an activist who spoke to He's wife, said the professor's three microblog accounts - on Sina.com, Sohu.com and QQ.com - had been closed after three recent postings alerting the public to Chen's plight.
Shen, a veteran journalist in Guangzhou who uses the pen-name Shi Feike, said his Sina Weibo microblog had nearly 100,000 followers before it was shut on Thursday night after he posted an item about the 10th anniversary of the unsolved murder of a Hunan teacher.
Shen said he began microblogging three years ago and in the past his microblog had only been suspended temporarily as a warning.
The online edition of Lianhe Zaobao, a Singapore-based Chinese-language newspaper which has been a popular news gateway for many mainland readers, has been inaccessible for at least three days.
Independent scholar Chen Yongmiao said the closure of Unirule's website and some popular microblogs was part of an ongoing crackdown on political discussion, regardless of whether the comments were coming from the right or left.
He said the crackdown had intensified because of a sense of political crisis following Bo's downfall and the need to assess the ramifications of Chen's escape from house arrest in Shandong province. Chen, a legal advocate who exposed forced abortions, is believed to be sheltering at the US embassy in Beijing.