Police rescued 41 suspected victims of human trafficking in the biggest operation of its kind in Bradford.
The vulnerable men, women and children were found as officers swooped on properties during the two-day operation.
Three men, aged 43, 33 and 28, and a 51-year-old woman were arrested on suspicion of fraud and human trafficking and have since been released on bail.
Warrants were executed at six addresses and 38 other addresses were visited where alleged victims were rescued. They include families of Eastern European origin.
Police joined forces with other agencies, including the Department for Work and Pensions (DWP), Bradford Council and the Hope For Justice charity to launch the operation on Wednesday - just days after information was received about human trafficking and fraud allegations.
It follows a separate human trafficking operation earlier this month at a Bradford pub in which nine women and a 15-year-old girl were rescued. Six men were arrested on suspicion of human trafficking and fraud offences and were later released on bail pending further inquiries.
The women and girl were taken to a local witness reception centre before being returned to their homes in Bradford.
Superintendent Vince Firth, Partnerships lead for Bradford District Police, said: “Human trafficking is a vile offence and West Yorkshire Police is committed to working closely with partners to tackle it. These recent operations in Bradford District, which have been carried out with partners including the Department for Work and Pensions, Hope For Justice and Bradford Council, have helped to locate a number of vulnerable people, who are now liaising with specially trained staff to ascertain whether they have been victims.
“We hope this will encourage people to inform the police if they have any suspicions of people being trafficked, as we need the support of our communities to be able to investigate this type of crime properly and bring any suspects to justice.”
The police chief reassured victims and urged anyone with information to contact police.
Supt Firth said: “Support networks are in place to help victims, and we would encourage them to come forward with any information which will help us to tackle this crime.”
Police are now investigating claims that the adults and children rescued in the latest operation were brought to the district for exploitation.
A number of people have been taken to witness referral centres to be seen by doctors, social workers and specially-trained police officers.
Human trafficking is said to be the fastest growing crime type in the world,
A DWP spokesman said: “DWP often investigates allegations of benefit fraud by working in partnership with organisations, including the Police, National Crime Agency and Home Office colleagues. This allows us to look into wider criminal activity and, where sufficient evidence is gathered, the full extent of the crime committed can be brought before courts.”