The owners ran the prison-like kilns with fierce dogs and thugs who beat the children at will, state television said. One accidentally killed a child with a shovel and buried the body at night, it said.
An army of 35,000 police in central China had so far rescued 217 people, including 29 children, the official China Daily reported today.
But state television said many more may be trapped, making bricks for little or no pay in brutal conditions in Shanxi and Henan provinces.
As many as 120 suspects had been detained.
"Now our conservative estimate is that at least 1,000 minors from Henan have been trapped and cheated into back-breaking work in these Shanxi brick kilns," a reporter from Henan said on the current affairs program Oriental Horizon.
The program showed workers who had been recently rescued – ragged, emaciated and mute and some bearing injuries.
But even amid the high-profile rescue effort, criticism is rising of official indifference to the poor farming families.
Local media reports and websites have cited what they say is a petition from fathers of boys kidnapped from Henan.
They complained that Shanxi police were unwilling to help Henan authorities to find and rescue the children.
"We are too weak and our children face constant threats to their life. We can only beg the government," said a copy of the document.
The China Youth Daily noted that local officials had apologised for failing to rescue the workers.
"But we have even more reason to ask why was it only after the case was widely reported by the media and shocked the central leadership that the local government then thought to apologise to these poor rural workers," it said.
"What were they doing before?"