Woman kept her "mentally ill child" locked up for years.

German police have discovered a woman being held captive by her mother for decades.

According to ITV, police discovered the woman after they were called out to a the flat in the Southern German city of Rosenheim to assist with an eviction.

Police broke down a locked door within the “rubbish-strewn flat” and found a 26-year-old mentally disabled woman who it’s alleged had rarely seen the outside world.

The mother has allegedly been keeping her mentally disabled daughter locked up since she was a young child, with police saying she was found in a “physically run down and neglected state”.

“Communication with her is very, very difficult,” said police spokesman Stefan Sonntag.

German police discovered the woman being held captive by her mother while attending an eviction. Source: iStock.

One neighbour, who has been living close to the apartment since 2003, claims to have never seen the girl.

Another told police the mother frequently refused any offers of help and said that the daughter could often be heard screaming and kicking the walls at night. The neighbour believes the daughter was locked up for at least five years.

"It's a truly tragic case," Sonntag continued.

While the daughter has since been sent to a psychiatric hospital for treatment and recovery, a 54-year-old woman believed to be her mother allegedly attempted suicide as soon as police entered the flat, throwing herself down a stairwell.

The mother is currently in hospital in a critical condition, but did not receive life threatening injuries from the fall. She is yet to be questioned by police.