Officials in China's southeastern Fujian province have detained seven petitioners in a "black jail" after they protested at the U.S. embassy over the Mid-Autumn Festival.
Separately, petitioners in south-central Changsha city say at least 21 people have been formally arrested after traveling to Tiananmen Square to air grievances.
The seven petitioners who traveled to Beijing from Fujian's capital Fuzhou, and from the port city of Quanzhou, were detained by police on their way to the U.S. embassy in the Chinese capital and were being held in a guesthouse under lock and key by officials from their hometowns, sources said on Wednesday.
"They are all being held at the Duxinyuan Guesthouse, Room 107," said a fellow petitioner surnamed Lin, citing a guesthouse in the Xicheng district of the city, near the North Railway Station. "They haven't [let them out yet]."
Lin said the petitioners were unable to make contact with the outside world. "They have taken away their identity cards," he said. "We often run into this sort of situation."
Wang Guozhi, the son of detained petitioner Wang Kui, said he had lost touch with his elderly mother after Tuesday morning.
The group had planned to go to complain to the U.S. embassy in Beijing about the loss of their land.
Wang Guozhi said he believed the petitioners were being held at several different locations.
"The [police] won't tell us anything," he said. "Where am I going to go to see them?"
Among the other petitioners being held was Lin Dongfa, protesting against repeated detentions and beatings of his son who had complained of official corruption linked to local pollution.
His son, Lin Yingqiang, said his father's mobile phone was turned off.
"I am very worried about my father's safety. He is over 80, and he has been seeking redress on my behalf," he said. "We have used every legal petitioning channel available ... and no one has done anything about it."
"We have been attacked and seriously beaten out of revenge instead," Lin said.
Sichuan-based rights activist Huang Qi said the group had been hoping to win international recognition over their plight.
"These people whom no one in China cares about should elicit the concern of the international community," Huang said. "This is very important, because they are taking a great risk [by going to the U.S. embassy]."
"The authorities can easily send ordinary people like them to labor camp or to prison."
Huang, who founded the Tianwang website to help petitioners and rights activists, said officials often retaliate harshly against anyone approaching foreign embassies with grievances, fearful that a trickle could turn into a flood.
Meanwhile, 21 petitioners from Changsha were formally detained by authorities there after they traveled to Beijing to campaign to get back property leased from their families when the Communist Party took power in 1949.
"All 21 of those who came back from Beijing have been detained," said fellow petitioner Wang Yuehui. "There were a few others who suddenly and mysteriously disappeared from their homes."
Wang said a total of 30 people were likely behind bars now and would likely face criminal charges.
"They went to Beijing, to Tiananmen Square," he said. "Originally they aimed to bring their case to the attention of the central government."
He said the group had chanted slogans near a ceremonial flagstaff on the square.
"They have already taken away ordinary people's homes. How are they going to live?" Wang said.
China already sees thousands of "mass incidents" across the country every year, according to official statistics, many of which are protests or sit-ins linked to forced evictions, allegations of corruption, and disputes over rural land sales.
Reported by Qiao Long for RFA's Mandarin service and by Wen Yuqing for the Cantonese service. Translated and written in English by Luisetta Mudie.