A Chinese province has said it will no longer send people to controversial "re-education through labour" camps for three types of political offences, state media reported Thursday.

A senior official in Yunnan, in the southwest, said people suspected of "undermining state security" and "smearing the image of top officials" will no longer be sent to the camps, the state-run Xinhua news agency reported.

Meng Sutie, the top justice official in the province, said the change would also apply to people judged to have "caused unrest" while making complaints about government officials, according to the report.

He added that Yunnan would "temporarily suspend" such sentences for other kinds of illegal activity as a prelude to national reforms.

Under China's re-education through labour system, police are empowered to send people to labour camps for terms of up to four years, leading to widespread rights abuses and use of the camps to punish political dissenters.

Chinese authorities have issued a number of statements suggesting major changes to the system will be made this year, with Meng's comments going further than any previous ones, but critics worry that such reforms may be merely superficial.

Four Chinese cities designated as "test sites" for measures have replaced re-education through labour with a system named "illegal behaviour rectification through education", the Beijing News reported.

The report did not detail differences between the two systems.

A 2009 United Nations report estimated that 190,000 Chinese were locked up in such facilities.

Most of those detained are believed to be held for petty crimes.

Life in the camps can vary widely, but many prisoners face extremely long work days manufacturing goods for international markets or doing agricultural work, the Duihua Foundation, a US-based rights group, said in a report.

The system, established in the 1950s, has come under vocal attack in Chinese media over the past year, but its abolition faces resistance from local governments who profit from products made by camp prisoners and lack other tools to keep social order.

Reforms to the re-education through labour system are not expected to require a suspension of China's forced drug rehabilitation camps, or its separate reform through labour prison system, which have also been targets for rights campaigners.