Seven Chinese nationals who smuggled Malawians to South Africa and subjected them to forced labour have been handed 20-year prison terms each.

The four men and three women were found guilty of human trafficking and kidnapping earlier this year by a South African court.

Their sentence comes nearly six years after they were arrested when local authorities raided a factory in Johannesburg and found 91 Malawian nationals, 37 of them children, working in appalling conditions.

Human trafficking is a major concern in South Africa, with the country regarded as a "source, transit and destination", according to the government.

The group - Kevin Tsao, Chen Hui, Qin Li, Jiaqing Zhou, Ma Biao, Dai Junying, and Zhang Zhilian - were found guilty on 158 of the 160 counts for which they were charged.

These include helping illegal immigrants remain in South Africa and violating the country's labour laws by failing to register their operations and and keep a record of their earnings among others.

The factory raid came after authorities received a tip-off from a worker who had managed to escape.

It later emerged that employees were forced to work 11-hour shifts, seven days a week, without proper training or safety equipment.

They were also paid far below South Africa's minimum wage of $1.64 (£1.22) per hour and had their pay docked if they wanted time off.

According to South Africa's labour laws, employees cannot work more than nine hours a day and are generally entitled to a "weekly rest period of at least 36 consecutive hours" that includes Sunday, unless a different agreement is reached.

One man testified that workers were not allowed to leave the heavily guarded factory premises, even to buy food, which he described as dirty and unsuitable for human beings.

According to authorities, the victims had been smuggled into the country in shipping containers.

Mr Tsao worked as a manager at the factory, named Beautiful City, while his co-accused were supervisors, according to local news site News24. The factory made inner cottons for blankets using recycled material.

South Africa's prosecuting authority welcomed the sentence, saying it would help "bolstering our fight against human trafficking".

"Human trafficking has become a scourge in our country, we have become a destination as South Africa for human trafficking [due to] various reasons, including our porous borders," spokesperson Phindi Mjonondwane said.

The department of labour, which was part of the raid in 2019, also welcomed the sentence handed down as it urged for greater collaboration between government departments to "root out all these issues".