An employee at a clinic for disabled people outside Berlin accused of killing four people and wounding a fifth was placed in urgent psychiatric care Thursday, a prosecutor said.

In a case of shocking violence that made national headlines, the slain victims, two women and two men, were stabbed with a knife late Wednesday at the facility in Potsdam, the daily Bild reported.

The victims were residents of the care clinic.

A 51-year-old female staff member was immediately taken into custody and state prosecutors sought a warrant for her arrest on suspicion of manslaughter from a local court.

However, Wilfried Lehmann, chief prosecutor in Potsdam, told AFP that the magistrate "ordered her placement in a psychiatric clinic" due to "pertinent evidence" of a mental illness. 

He declined to offer further details on the killings so as not to jeopardise the "investigation which is still getting started".

A spokeswoman for the state prosecutors had said earlier that the killings did not bear the "characteristics of (premeditated) murder" while police said the dead were subjected to "intense, extreme violence". 

State police were called to the clinic at around 9pm 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 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 candles in honour of the dead at the clinic, as police maintained a strong 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.