Indian police say they have found 17 weakened people in a raid on a house believed to be at the centre of an illicit blood donation scheme.
Syringes and blood bags were also found at the farm in Uttar Pradesh state.
The donors were impoverished migrant workers. Some of them are said to have been giving blood for up to two years.
It is unclear if they were held against their will. Five arrests have been made over what is alleged to be a scheme to supply blood to nearby hospitals.
Another two suspects - named as Pappu Yadav and Jayant Sarkar - are being sought in the case, police chief Piyush Mordia told the BBC.
The police raided the property in the eastern district of Gorakhpur on Saturday but news of it has only just emerged.
'Risk to patients'
Mr Mordia said the farm originally held 25 people from the states of Uttar Pradesh, Bihar, West Bengal and Orissa.
Some of them escaped while others stayed back.
"These 17 people seem to have the life sucked out of them," Mr Mordia said.
"They could barely stand and on medical examination their haemoglobin levels were found to be very low.
Donors questioned by police said they had been lured with the promise of employment.
They were reportedly told they were being paid 300 rupees ($7; £3.7) every time they gave blood.
However, they only received 50 rupees ($1; £0.6) in hand each time and were told the rest of the money had been paid into bank accounts.
Mr Mordia said the police were trying to find out where the blood had been supplied to.
Patients who may have received the blood could be in danger, he said.
Laboratory technicians from nursing homes had helped set up the illicit operation, police said.
They said the bags in which the blood was collected had been labelled to appear authentic.