Forty-eight people who were allegedly to have been involved in the illegal use of slave labors were detained in Shanxi, while the others were detained in Henan, according to local police sources.

By Saturday, 351 people, including 22 under the age of 18, were freed after police stormed more than 3,700 small brick kilns and coal mines, many of them are unlicensed, in Shanxi, the country's biggest coal producer.

Heng Tinghan, a 42-year-old foreman of a brick kiln in Hongtong county in Shanxi was arrested Saturday after the Ministry of Public Security issued a wanted list of the second-highest importance for him.

Heng was suspected of forcing people to work as slaves in his brick kiln since March 2006, among whom one died and 20 were injured under the extremely cruel working conditions.

In central China's agricultural province of Henan, a major source of salve workers, police have detained 120 suspects in the campaign.

Police have freed 217 forced workers, including 29 aged under 18 and ten mentally-handicapped persons, according to Henan provincial public security bureau.

Five gangs involved in organizing salve workers for the brick kilns, in Zhengzhou, capital of Henan, have been busted and their 13 members were arrested.

The use of slave workers came under spotlight after an open "call-for-help" letter posted on the Internet earlier this month by more than 400 parents in Henan who believed their missing children have been sold to the small brick kilns as slave workers.