Three suspected slave masters have been arrested after 20 people were rescued in a raid at a factory.
The people were working 80-hour weeks for just £25, producing pictures and frames for a number of major high street companies, police said.
Three men aged 51, 43 and 40 were arrested on suspicion of a forced labour conspiracy and of human trafficking after the factory in Rochdale, Greater Manchester, was raided.
Officers said the workers - who also complained of being physically attacked by their employers - were paid £125 each for their week's work, but were then forced to hand back £100 for rent and travel, leaving them barely any money to survive.
A 24-year-old man was also arrested on suspicion of immigration offences.
Seven people have been arrested in Greater Manchester as part of a probe into child sexual exploitation.
Six men and a teenage boy are being questioned on suspicion of conspiracy to commit sexual acts with a child.
The arrests took place following raids in the Rochdale and Oldham areas.
Police said the suspects, aged between 16 and 47, were of mixed ethnicity.
Detective Chief Inspector Andy Aston said: "The team were initially looking at reasons why two girls, aged 15 and 13, and a 13-year-old boy were going missing from home.
"Officers spoke to one of the girls who suggested they were being groomed between 16 September and 17 October 2014.
"A swift investigation was launched and agencies worked together which has resulted in these arrests across the Rochdale and Oldham areas plus the safeguarding of three vulnerable children."
The long awaited report into child sexual exploitation in Rochdale has been criticised by a health worker who helped to expose the scandal.
Sara Rowbotham has called for a full national inquiry into child grooming as she says the report, by MP Ann Coffey, doesn't go far enough in holding police and social services to account.
A former health worker in Rochdale has told ITV News there should be a full national inquiry into child grooming.
Sara Rowbotham helped convict nine Rochdale men of child sex abuse.
Ms Rowbotham says that a report today into the failure of police and prosecutors to catch more abusers, doesn't go nearly far enough.
ITV News Senior Correspondent Emma Murphy reports:
The Prime Minister has called for "very early intervention" in cases where police and social services suspect child sexual exploitation.
"Those agencies, particularly the police and social services who often know about these people and know what is happening, they need to intervene and act more quickly," David Cameron said at a Q&A session in Cheshire.
Prime Minister David Cameron has said one of the biggest lessons to learn from the child sexual exploitation report is that "very early intervention" is needed.
ITV News Producer Vincent McAviney reports:
Rochdale MP Simon Danczuk has told ITV News the child sexual exploitation report "doesn't go far enough".
Echoing the comments made by Rochdale whistleblower Sara Rowbotham, Mr Danczuk said, "If she says this report doesn't go far enough then that's good enough for me."
He said the report, led by Stockport MP Ann Coffey, was "really attempting to shift the blame away from the perpetrators and away from the police, and towards public opinion."
"There is certainly a need to learn [from abuse cases] across the country as a whole," the MP added.
The health worker who was key in bringing the 2012 Rochdale child sex abuse case to trial has called for a full national inquiry into child grooming.
Sara Rowbotham claimed today's report into child sexual exploitation in Greater Manchester does not go far enough, and stressed that both police and social services should be held to account.
ITV News Senior Correspondent Emma Murphy reports from Manchester:
The health worker responsible for gathering the main evidence in the 2012 Rochdale child sex abuse case has told ITV News Ann Coffey's report "doesn't go anywhere" to ensuring it never happens again.
Sara Rowbotham said she had "tried hard to make it clear" to the authorities that children were being sexually exploited but that "nobody did anything meaningful" to stop it.
"Ann Coffey's report doesn't go anywhere to address any of that, it doesn't go anywhere to ensuring that that's never going to happen to anybody again," the whistleblower said.
"She doesn't offer concrete solutions, she doesn't absolutely say we have zero tolerance, it doesn't go anywhere to address the injustice and the absolute terror that happened to those children in Rochdale," she added.
Stockport MP Ann Coffey, who led a report into child sexual exploitation, has said the authorities' response to abuse "shouldn't be a postcode lottery".
ITV News Granada Political Reporter Daniel Hewitt reports:
"Response to child sexual exploitation shouldn't be a postcode lottery." Children move around, she says. Police teams need to work closer.