Hong Kong (CNN) -- China's move to abolish re-education through labor camps -- under which tens of thousands have been imprisoned without trial -- may be no more than a cosmetic change, a new report from Amnesty International warns.
The human rights group says that while labor camps are being shut, research suggested that authorities are expanding the use of "black jails," enforced drug rehabilitation clinics and "brainwashing centers" to take their place.
"There is a very real risk that the Chinese authorities will abolish one system of arbitrary detention only to expand the use of other types," the report said.
A spokesman from China's Ministry of Justice declined to comment on the Amnesty report.
Corinna-Barbara Francis, Amnesty International's China researcher, said the abolishment may only be a "cosmetic change just to avert the public outcry over the abusive re-education through labor system."
China said on November 15 that it would close its labor camps after earlier putting the policy under review, with the move hailed as the biggest change to China's criminal justice system in decades.
Detention without trial
The system was set up in 1950s and allows police to detain petty offenders -- such as thieves, prostitutes and drug addicts -- for up to four years without a trial.
According to China's Ministry of Justice, the country had 351 labor camps at the end of 2012, with more than 50,000 inmates. Other estimates have put the number of detainees much higher.
The "re-education process" has also been used to punish those detained for their political, religious or personal beliefs -- such as members of the banned Falun Gong spiritual movement or petitioners with complaints against local officials, Amnesty said.
Torture is said to be rife at the camps.
Detainees have told Amnesty International they were beaten, sometimes with electric batons, denied food, subjected to simulated drowning, injected with unknown drugs and subjected to the "rack" torture."
The report said interviews with petitioners and Falun Gong practitioners revealed abuses were continuing despite the closure of the camps.
Some labor camps were being re-labeled as drug rehabilitation centers and released detainees were being sent to black jails -- unofficial detention centers set up in places like hotels or abandoned buildings -- or "brainwashing centers," another form of arbitrary detention.
Falun Gong practitioner Zhang Zhi told Amnesty International she was released from a labor camp in Harbin in June 2013 but on her release staff from a brainwashing center were waiting for her at the gate. Her family were able to intervene and prevented her from being taken away. She has since gone into hiding.
"The Chinese authorities must immediately end all forms of arbitrary detention and ensure that laws protecting detainees are brought into line with international human rights standards," Francis said.
"This needs to be a fundamental change in the policies that are at the root of the repression and which strip detainees of their most basic rights."