The police have rescued 300 people locked in a rice-processing factory and forced to work throughout a coronavirus lockdown.
From the end of March the men were allegedly not allowed to leave the mill in the northern city of Kano.
Five managers at the Indian-owned mill called Popular Farms have been arrested.
The police were tipped off about the men’s plight after one of them called a human rights organisation.
“What I saw was heart breaking. Where the company kept these people to live isn’t fit for animals,” Karibu Yahaya Kabara of the Global Human Rights Network told the BBC.
“Their meals weren’t enough and there were no drugs for those that took ill,” he said.Mr Kabara said his organisation was taking up the case to ensure that the men got justice.
Nigerian businesses were asked to close up shop in late March as part of government guidelines to halt the spread of coronavirus.
Police spokesman Abdullahi Haruna told the BBC that the plant had now been shut down and the owners were being investigated for “holding the men against their will”.
Some of the men say were forced to work most of the time during their incarceration, with little food.
“We were allowed to rest for only a short time, no prayers were allowed, no family visits,” 28-year-old Hamza Ibrahim, one of those rescued, told the BBC’s Mansur Abubakar in Kano.