China is investigating whether hundreds of children, most between the ages of nine and 16, were sold to factories in the southern province of Guangdong over the past five years to work as virtual slave labourers, state media said Wednesday.

The probe was launched following the publication Monday of an investigative report by Southern Metropolis, a state-run daily in Guangdong. The report said the children were "sold like cabbages" by their parents to gangs who in turn sold them off to employment agencies or directly to factories hundreds of kilometres from their homes.

Most of the kids were from Liangshan, a poor farming town in southwestern Sichuan province, and ended up working in electronics and other factories in Guangdong's Dongguan city as well as Shenzhen and Huizhou, the paper said.

The official China Daily newspaper on Wednesday quoted Dongguan spokesman Wang Yongquan as saying that the city's "labour enforcement and trade union will investigate all companies in the town, the labour market and agencies."

He told the paper that police already had rescued more than 100 youngsters from rented houses and arrested several people but gave no additional details.

The probe comes less than a year after Chinese media uncovered that children as young as eight were abducted or recruited from bus and train stations with false promises of well-paying jobs and sold to brick kilns in several northern Chinese provinces for about $65 US.

The victims were forced to work almost around the clock, beaten, and deprived of pay, nourishment and basic medical care.

The Southern Metropolis said the children from Liangshan earned as little as 30 cents an hour and were forced to work long hours.

The Guangzhou Daily described tagging along with police in Dongguan Tuesday as they questioned young factory workers. One girl named Luo Siqi from Liangshan said she made 50 cents an hour and initially claimed she had come to Dongguan on her own.

When told by police that the money she thought she was sending home could not have reached her family, she broke down in tears, the paper said.

"My father and mother sold me. I don't want to go back," Luo was quoted as saying.