POTSDAM (AFP) - An employee at a clinic for disabled people outside Berlin was arrested Thursday (April 29) on suspicion of killing four people at the centre and wounding a fifth, police said, with the motive still unclear.

The slain victims, two women and two men, were stabbed with a knife late Wednesday at the facility in the city of Potsdam, the daily Bild reported.

Those killed are believed to be patients at the care clinic, local newspaper Potsdamer Neueste Nachrichten reported.

Police said earlier the dead were subjected to "intense, extreme violence", but did not give any details around the circumstances of the killings.

A 51-year-old female staff member has been arrested on "strong suspicion" of carrying out the assault, police said, while acknowledging that any motive was still undetermined.

Prosecutors were due to give a news conference later in the day.

State police were called to the clinic at around 9 pm Wednesday, according to reports, with the victims later discovered in their rooms. Specialised teams were dispatched overnight to collect evidence from the crime scene.

'Incomprehensible act'

The clinic, run by the Lutheran Church's social welfare service, specialises in helping those with physical and mental disabilities, including the blind, deaf and severely autistic patients.

It offers live-in care as well as schools and workshops. Around 65 people live at the facility, which employs more than 80 people.

Potsdam is the capital of Brandenburg state, whose premier Dietmar Woidke said he was "shocked by this horrible news".

"My thoughts are with the victims and their loved ones," he said, calling it a "difficult day" for the region. Potsdam mayor Mike Schubert called the crime an "incomprehensible act".

Local residents began leaving bouquets of flowers, cards and lighted candles in honour of the dead at the clinic, as police maintained a large presence outside.

A ceremony in memory of the victims is planned for Thursday evening, said Matthias Fichtmueller, the clinic's theological director.

"We are stunned," he said. "When the case has been wrapped up in the criminal justice system, we will still have to live with the wounds." Germany has seen a number of high-profile murder cases from care facilities.

In the most prominent trial, nurse Niels Hoegel was sentenced in 2019 to life in prison for murdering 85 patients in his care. Hoegel, believed to be Germany's most prolific serial killer, murdered patients with lethal injections between 2000 and 2005, before he was eventually caught in the act.

And in October, a Polish healthcare worker was sentenced to life in prison in Munich for killing at least three people with insulin.