Chinese authorities detained or placed under house arrest more than 60 dissidents in July, according to a Hubei-based rights group.
The China Human Rights Observer said in a report that it had received 61 reports of detentions, enforced "holidays," and other forms of surveillance, as well as labor camp sentences.
It said the crackdown would likely intensify in the run-up to the 18th Congress of the ruling Communist Party later this year.
"Under the current situation, in which China is focusing on so-called stability, China's human rights situation is getting worse and worse," said Liu Feiyue, founder of the group and author of the report.
"They are taking a whole series of measures against dissidents, rights activists, and petitioners, ranging from depriving them of liberty to sentencing them to labor camp or to prison," Liu said.
"I personally am also a victim of [these measures], and I have been placed under long-term surveillance and also 'disappeared' by them," he said.
'They will retaliate'
He cited the sentencing to labor camp of Heilongjiang activist Liao Cheng, along with Hunan activist Xiao Yong. Meanwhile, Liu Benqi, an activist in the far western province of Qinghai was placed under administrative detention, he said.
Guangdong-based rights lawyer Tang Jingling had been summoned and warned by state security police, while Beijing-based activist Wang Lihong had been forced to "take a trip" to an undisclosed location.
Liu added that the disappearance of Anhui-based activist Zhang Lin was also causing concern.
"[Beijing-based activist] Wang Lihong ... was taken on a trip on July 21," he said. "They will retaliate against you [if you don't comply]."
He said Beijing-based unofficial Protestant "house church" pastor Li Fenggang was currently in police detention at the city's Fuwai Hospital, where he was undergoing treatment for a heart condition.
"My heart disease recurred," Li said in an interview on Thursday. "They asked me how it happened and I told them that it happened in the basement of the police station when they were pouring water over me."
Li said he was still concerned for his safety in hospital, however.
"I have told the relevant authorities and my friends about this because I don't want to meet the same fate as Li Wangyang," he said, referring to the veteran 1989 labor activist who died while in hospital in police custody in early June.
"If anything unusual happens to me, the police are in the hospital with me right now, so there will definitely be a connection," he said.
Meanwhile, retired Shandong University professor Sun Wenguang said he thought the controls on activists were much harsher than last year, when China was in the midst of a security clampdown following online calls for a "jasmine revolution" sparked by recent uprisings in the Middle East.
"There have been people there [watching me] around the clock since May 16," Sun said. "The state security police are watching me, and they place strict controls on me if I try to go out."
"I'm not allowed to visit my friends," he said. "I have never been in this situation for such a long period of time at a stretch before."
Reported by Qiao Long for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.