Authorities in the southern Chinese city of Guangzhou are continuing to hold a top human rights lawyer with no announcement of criminal charges against him, in spite of a vocal campaign for his release, activists said Thursday. Yang Maodong, better known as Guo Feixiong, was criminally detained on Aug. 8 on charges of "incitement to disturb public order," after being involved in anti-censorship and anti-corruption protests. "The authorities have made one arrest after the other in recent months, and this is still going on," said Beijing-based fellow activist and poet Wang Zang, who was among dozens of campaigners who signed a public petition calling for Guo's release. "This is human rights violation on a massive scale." Wang said those who signed the letter were angry at the ongoing crackdown on activists who have called since March on the highest-ranking ruling Chinese Communist Party leaders to reveal details of their assets, and those of their families. "We wanted to protest this political oppression, but also to reiterate that Guo Feixong is innocent, and should be released immediately," he said. "None of us is safe, and any one of us could be next." Corruption activist Guo was released from jail in September 2011 following a five-year jail term and has previously been subjected to extrajudicial detention and torture. The rights lawyer, whose wife and two children were granted political asylum in the United States in 2009, rose to prominence during a 2005 campaign by the people of Guangdong's Taishi village to recall their elected chief amid allegations of corruption. He was sentenced to five years' imprisonment in 2006 by a Guangdong court for "illegal business practices" after repeated beatings and detentions did little to deter his rights campaigns. Detained civil rights activist Xu Zhiyong, who is being held at a Beijing detention center on public order charges after calling on China's leaders to reveal their assets in March, had recently called on ordinary Chinese to take a stand to protect the rights of citizens. President Xi Jinping has launched a nationwide clampdown on corruption, warning that the Communist Party must beat graft or lose power. However, police continue to detain activists who call for greater transparency. The overseas-based Chinese Human Rights Defenders (CHRD) said last week it has confirmed the criminal detentions or disappearances of 58 individuals in the ongoing crackdown on anti-corruption activists, half of whom have been formally arrested. Authorities in Beijing are preparing to try anti-graft activists Yuan Dong, Zhang Baocheng and Ma Xinli for "unlawful assembly" after they held up banners in the street calling on officials to disclose their assets in late March. Hubei activist Liu Jiacai, Shenzhen-based activist Yang Mingyu, known as Yang Lin, and Hunan-based activist Li Huaping, known by his online nickname Nuowei Senlin are also being held in detention centers for similar activities. 'Gray economy' China's hidden household income-otherwise known as its "gray economy"-has topped 6.2 trillion yuan (U.S. $1 trillion) or about 12 percent of the world's most populous nation's economic output, a new report says, indicating a widening wealth gap fueled by corruption. The state-backed China Reform Foundation report, which provided the 2011 figures, said most undeclared income in the Chinese economy is undocumented and is held in the hands of relatively few people, according to Caixinmagazine this week. The richest 10 percent of urban Chinese made an average income of 188,000 yuan (U.S. $31,000) in 2012, more than three times the officially reported income level. According to the study, rich city-dwellers have an income around 21 times that of the poorest Chinese, compared with an officially reported factor of 8.6. Widespread mismanagement of public funds, loose monetary policy and lax enforcement of regulations were to blame for the growth of China's hidden economy, the report said. It said state-sponsored monopolies, rampant public sector corruption, and a lack of effective public oversight had contributed to the problem. UPDATE: 27/ 11/ 2015 Chinese rights activist jailed for 6 years A prominent Chinese rights activist, Guo Feixiong, was sentenced to six years imprisonment on Friday by a court in southern China, amid a continuing crackdown on human rights advocates across the country, his lawyer said on Friday. Two other activists, Liu Yuandong and Sun Desheng, were sentenced to three years and two-and-a-half years respectively, according to Guo's lawyer, Zhang Lei. Guo and Sun had been accused of "gathering crowds to disturb social order" during a nearly week-long peaceful demonstration outside the gates of a newspaper, the Southern Weekly, in January 2013. The protest called on authorities to respect media freedom amid a censorship row. "He wasn't guilty of anything at all. This sentence is unacceptable and unfair," Zhang told Reuters by telephone after attending the court on Friday. Guo had previously been jailed for nearly five years for his grassroots activism. Guo, 48, whose real name is Yang Maodong, had been detained by Chinese authorities for over two years before sentencing, with his trial stuck in limbo due to delays and a boycott by his lawyers last year to protest what they called procedural violations. As with previous hearings for Guo, and other rights activists in Guanghzou, the area around the court was blocked off and heavily policed. Guo had been held in a crowded cell, and barred from exercising outside in violation of international standards on the treatment of prisoners, according to rights groups. His lawyer said Guo's health had deteriorated and that two police officers had handled his Guo roughly in court, injuring his arms. Amnesty International said Sun Desheng had been forced to wear handcuffs and leg cuffs for long periods in detention. Human rights groups and Western countries have expressed repeated concern about a widening campaign by President Xi Jinping to quash dissent among academics, journalists and social activists. A Chinese court on Thursday upheld a conviction against a prominent journalist, Gao Yu, 71, who was accused of leaking an internal Communist Party document to a foreign website but reduced her seven-year jail term by two years. "Beijing's assault on civil society seems to know no bounds as peaceful activists are increasingly subject to criminal prosecutions," said Sophie Richardson, China Director at Human Rights Watch in New York. "The Chinese government should immediately drop all charges against Guangzhou activists Guo Feixiong and Sun Desheng and release them."