Stripped naked and beaten, Peng Hong's memories of his time in a Chinese "re-education" labour camp are dark -- but even so, he greeted Beijing's abolition of the widely-loathed system with only cautious optimism.

The closure announcement came in a package of reform pledges by the ruling Communist Party three days after a key gathering called the Third Plenum, and one year after new leaders under Xi Jinping took power.

But as with other sweeping pledges revealed late Friday -- including changes to the one-child policy, farmland ownership rules, and access to urban social services -- implementation will be key.

"Abolishing it is better than not abolishing it," former prisoner Peng, 38, told AFP by phone. "I am cautiously optimistic."

Under "re-education through labour" citizens could be sentenced to labour camp for up to four years by a police panel, without appearing before a judge.

The system -- introduced in 1957 to deal with minor offenders faster -- became rife with abuse.

Some local officials used it to silence "petitioners" seeking to complain about them to higher-level governments, along with others perceived as undermining the ruling party's control on power.

Peng was sentenced to two years in 2009 after forwarding a cartoon online mocking a crime crackdown launched by Bo Xilai, the then-powerful head of his southwestern hometown of Chongqing.

Police visited him one evening and six days later he was standing naked and bent over before stick-wielding guards who beat anyone who looked up. His only daughter was born five months into his term, with family visits just every few months.

"I have very bad memories from that time," Peng said. "If I go back and think about it then my whole mood changes, those times were so dark."

Pressure for reform has been building for years, and the problem was driven home in August last year when Tang Hui, a mother in the central province of Hunan, was sentenced to 18 months after petitioning repeatedly for justice for her daughter, who in 2006 at age 11 was kidnapped and forced to work as a prostitute.

Following a public outcry, Tang was released after just over a week, and earlier this year won 2,941 yuan ($483) compensation.

Even before her case erupted, "I think a lot of people already knew that the system was unfair," she told AFP Saturday, adding she was "happy" it would end.

Those who would have been eligible for the camps will still face punishment in future, said Randy Peerenboom, a Beijing-based law professor with La Trobe University in Melbourne, perhaps through other systems such as 15-day administrative detention or the criminal code.

"I don't think it's going to have any major changes on the fates of the majority of people who were subject to re-education through labour. They are still likely to be detained and subject to some penalty or the other," he said.

China's criminal code now allows for courts to impose lighter punishments suitable for petty offenders, from three to 24 months' house arrest and one to six months in a police detention facility, the official Xinhua news agency said.

Beijing-based rights lawyer Pu Zhiqiang said the criminal system would be "relatively a little better".

"Before there was absolutely no legal basis and no need to go to trial," he said. "You could have them gone in a week, never mind letting them see a lawyer.

"Now if you detain people you have to hold them and find a charge," he said.

Yet China's legal system -- despite improvements towards the often-stated national goal of establishing the rule of law -- remains riddled with abuses, from confessions extracted through torture to lack of legal aid to wrongful judgments.

Party leaders at the Third Plenum pledged to work on those issues as well "to improve human rights", Xinhua said.

The US-based campaign group Human Rights Watch warned against exchanging re-education through labour for another problematic scheme.

"This important step will only be meaningful if the government ensures that what comes after it does not institute another system of detention without trial," Asia director Brad Adams said in a statement on Saturday.

But he also acknowledged that "the Chinese government has finally responded to years of international and domestic criticism".

Since taking power a year ago, the new Communist leadership had hinted at changes to re-education through labour.

But they have also tightened control of public voices that they felt threatened by, Pu said, calling the trend "pretty disappointing".

"It will be a long road to building a country that follows the rule of law," he said.