An eight-year-old boy and his stepmother were released on Monday after being detained for allegedly disturbing social order at the train station in Guangzhou, Guangdong Province on Sunday.

The stepmother, who refused to give her name, was taken away from the station when she tried to petition against the treatment her stepson has received while he was allegedly being detained for four years in a "black jail," Chen Keyun, the lawyer representing the boy told the Global Times on Monday.

The boy, surnamed Chen, had been reportedly detained in a "black jail" allegedly run by local officials in Zhuhai.

He was only released one month ago and had lost his ability to talk. He was then taken to Beijing for medical treatment, said the lawyer.

A "black jail" is widely known as an illegal place to hold petitioners.

A source close to the family told the Global Times that the boy was detained because his father, Chen Fengqiang, a retired and disabled soldier, had been petitioning after his house was demolished. The boy's biological mother has been missing for days, said the source.

Zhuhai police said via Sina Weibo that an investigation had started, refusing to reveal any details of the "black jail."

"We will let the public know if there is any update," a press officer told the Global Times.

A police officer from the Guangzhou train station said the mother, who was holding a banner giving details of her stepson's experience, attracted crowds and disturbed social order.