The major Chinese city of Guangzhou will empty its hard-labour camps by year's end, state-run media said Monday, as some localities phase out the unpopular punishment.

Critics say "re-education through labour", known as "laojiao" and which lets police issue sentences of up to four years without a trial, is open to abuse.

Some cities or provinces are moving away from laojiao while Premier Li Keqiang in March promised some reforms this year, although concrete nationwide steps have yet to be announced.

"All (100 or so) detainees in Guangzhou labour camps will have completed their sentences and be released by the end of the year," the China Daily reported, citing a senior judge in the southern city.

Guangzhou is the capital of Guangdong province, which stopped taking new re-education through labour cases in March, it added.

In February the southwestern province of Yunnan said it would no longer send people to labour camps for three types of political offences.

Four cities designated as testing grounds have replaced the system with an "illegal behaviour rectification through education" programme, domestic media said at the time, without providing details.

The laojiao system was set up in the 1950s and targets often include anti-government petitioners, drug users and other minor offenders.

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