The closure of China's "re-education through labour" camps is likely to have minimal benefit because of other rights abuses, Amnesty International says.
Arbitrary detention will persist in drug rehabilitation centres and other facilities, the rights group said in a report on Tuesday.
The "re-education through labour" scheme, known as laojiao, was first instituted in the 1950s by the ruling Communist Party, which announced last month it planned to dismantle the system.
But Amnesty said there was a risk the Chinese authorities would replace te camps with other types of arbitrary detention.
Its report was based on more than 60 interviews conducted over the past four years with former labour camp inmates and other detainees, "most of whom were subjected to torture and other ill-treatment in detention", the group said.
A number of labour camps in Xinjiang, Jiangsu, Sichuan, Jilin and other provinces had been renamed as drug treatment centres offering "very little in the form of drug rehabilitation", the report said.
They were operating "virtually identically" to laojiao facilities "where detainees can be held for years of harsh forced labour and ill-treatment".
Under the re-education through labour scheme, police panels sentence offenders to up to four years in camps without a trial.
The United Nations estimated in 2009 that 190,000 people were held in the system, which is largely used for petty offenders but is also blamed for rights abuses by officials seeking to punish "petitioners" who try to complain about them to higher authorities.
Pressure to change the unpopular system has been mounting for years, and China's Communist Party leaders announced after a key gathering in Beijing last month that they would move to abolish it.
But they have so far released few details of how they plan to implement the change.
The Standing Committee of the National People's Congress, China's parliament, is expected to take up the issue next week, the state-run Xinhua news agency reported.
