China has pledged to bring to justice traffickers who enslaved hundreds of children and adults to work in brick kilns in two provinces.
Chinese TV shows malnourished and injured former slaves
As it prepared to send investigators to Henan and Shanxi, the government said that all captives would be freed.
Some 550 people have been liberated in recent weeks and families believe up to 1,000 children were enslaved.
The story made national headlines after parents of some of them launched an internet campaign for their freedom.
Children thought to be as young as eight years old were kidnapped, held captive and forced to work long hours for no pay.
The case has revealed the dark side of China's booming economy with forced labour and human trafficking common in rural areas, the BBC's Dan Griffiths reports from Beijing.
Responding to calls for action by President Hu Jintao and other senior top politicians, the labour and social security ministry vowed to send a team of investigators to the two provinces.
"The team will find out the truth as soon as possible, and we will go all out to rescue the workers who have been forced to work as slaves in the brick kilns," a deputy minister, Sun Baoshu, was quoted as saying by the Chinese state news agency Xinhua.
"The criminal offenders will be dealt with to safeguard the legal interests of the workers."
Thousands of police have been checking building sites in the two provinces and have made scores of arrests, Chinese media report.
Provincial authorities in Shanxi have also said they will punish officials for dereliction of duty unless all abused workers are freed within 10 days.
The wife of one kiln-owner arrested by police said that officials had previously done nothing about the kilns other than ask for money from her husband.
"The officials said that we were illegal and so they came for money but they didn't do any more than that," Zhang Mei told Reuters news agency in Hongtong, Shanxi.
She also blamed a Hongtong foreman, Heng Tinghan, who had allegedly found workers and controlled them directly and is now wanted by police.
"We really didn't know they weren't getting money," Mrs Zhang said.
State TV reports prison-like conditions in the kilns where slaves were controlled with beatings or fierce dogs.
Some young male workers were shown to have festering wounds on their feet and waists, possibly from being burnt by the kilns where they worked.
Many labourers were reportedly abducted off the streets of regional towns and sold on for as little as 500 yuan ($66, £33), the AFP news agency reports, quoting Chinese press.