Rights groups claim secret prisons, or 'black' jails, are sprouting up on the mainland in a campaign by regional authorities to purge petitioners. Accusations by rights groups of petitioners being secretly imprisoned have been circulating for two years. Evidence of the secret prisons' existence has now come to light after a group of Beijing activists carried out a series of rescue missions from late last month to free petitioners locked up in a black jail attached to a run-down budget hotel in Beijing. People in search of justice or with little faith in the lower-level justice system often try to take their grievances to higher authorities in big cities like Beijing. But they are regarded as an embarrassment by lower-level governments and are often subjected to physical abuse and mental torture at the hands of police. Xu Zhiyong , a law lecturer at Beijing University of Post and Telecommunications, said he discovered the black jails after receiving text-message appeals for help from several petitioners locked up in a room at the Youth Hotel in Taiping Street, near Taoranting Park. Dr Xu said when he and a number of activists arrived at the jail, about 30 petitioners, most from Henan province , were confined there. Wang Jinlan , a 46-year old petitioner from Pingdingshan , said she was locked up for two days before being freed on September 22 with the activists' help. Ms Wang said about 30 petitioners were still there after she was rescued. Calls to the youth hotel went unanswered yesterday, but the hotel is one of four known black jails believed to have been set up by authorities in Henan in league with unscrupulous hotel operators and thugs. They lock up petitioners temporarily before they are repatriated to their home towns. Investigations by the activists found that hotel operators were offered 150 yuan (HK$170) a day for each petitioner - compared to the 120 yuan they charge regular guests. The hotel operators and the thugs they hire serve as enforcers at the facilities. Repeated calls to the Bureau of Letters and Visits in Henan, a provincial-level office in charge of petitioning, were not answered yesterday. Ren Gaochao , a provincial government spokesman, said he was not aware of such facilities, but would look into the accusations. It is not known how many such facilities exist in Beijing and whether any government agency authorised them, but the black jails appear to be a tactic by authorities to clamp down on petitioners since the abolition of custody and repatriation centres. The system was scrapped after public outrage over the death of a young graphic designer, Sun Zhigang , in a Guangzhou custody centre in March 2003. Sun was taken into custody for failing to produce a residence permit and was later beaten to death. The black jails fill the vacuum left by the abolition of the custody centres. Dr Xu said detentions without due judicial process were a flagrant violation of human rights. 'The black jails are even worse because they amount to illegal imprisonment,' he said. Dr Xu, who has been beaten up several times in confrontations with hotel managers and thugs, said he believed there were more such black jails set up by regional authorities in Beijing, and he would continue to expose them. 'We'll fight the cancers until they disappear,' he said.