10's of thousand would be a reasonable guess on violent riots. Not limited to Human Rights-
Lots are over worker's rights and safety, land living conditions etc.
Protests and Demonstrations Numbers in China
The number of reported "mass incidents" rose from 8,700 in 1993 to more than 90,000 in 2006, according to the Chinese Police Academy. There were about 180,000 in 2010, according to Sun Liping, a Tsinghua University sociologist. According to the New York Times authorities recorded 127,000 so-called mass incidents in 2010 but most were too small to gain wide notice. According to figures from the China Academy of Social Sciences fights over land account for 65 percent of rural “mass conflicts” and is also a serious problem in cities.
The Guardian reported: "To some extent, the exponential increase is because of improved reporting of incidents that once would have been buried by the state press. Nowadays, the minute a window is smashed, somebody will whip out a cellphone camera and shoot a video that quickly is posted on a blog. The surge also reflects a public that is better informed and more active in seeking redress for grievances. [Source: The Guardian, December 23, 2011]
According to official statistics, there were 74,000 mass incidents in 2004 with a total of 3.7 million citizens taking part. In 2005, the number of mass incidents with at least 15 participants totaled 87,000. more than 200 a day, involving over four million Chinese. They included protests over unpaid wages, taxes, lay offs, land seizures, factory closings, poor working conditions, environmental damages, corruption, misuse of funds, ethnic tensions, use of natural resources, forced immigration and police abuse. Some of them have been quite large and violent. In addition to the mass incidents, lone individuals are increasingly adding to protest incidents.
China saw almost 90,000 such “mass incidents” of riots, protests, mass petitions and other acts of unrest in 2009, according to a 2011 study by two scholars from Nankai University in north China. Some estimates go even higher. That is an increase from 2007, when China had over 80,000 mass incidents, up from over 60,000 in 2006, according to an earlier report from the Chinese Academy of Social Sciences. There were 120,000 mass incidents in 2008, according to China’s Public Security Ministry.[Source: AFP, August 13, 2011]
The number of mass incidents rose from 10,000 with 730,000 participants in 1994 to 74,000 with 3.8 million participants in 2004. In 2000, there were about 40,000 protests, including 230 incidents of mobs laying siege to Communist Party offices in 82 cities, resulting in 5,500 casualties. In 2003 the government admitted to 58,000 incidents. The number of "incidents” was around 23,000 in 2006.