A Syrian man has been taken into psychiatric care a day after allegedly injuring four people in a knife attack on a German train, officials said Sunday, ruling out a terrorist motive.

The 27-year-old suspect is believed to have acted alone in the incident that started on a high-speed train between the Bavarian cities of Regensburg and Nuremberg shortly after 9:00 am on Saturday.

Two male passengers aged 26 and 39 and two others aged 60 suffered head and upper body injuries from the stabbings. 

The two younger men remain in hospital, Oberpfalz police vice-president Thomas Schoeniger told reporters.

"There are no indications of an Islamist background" to the attack, said Oberpfalz criminal director Sabine Nagel, but stressed that the investigation was still in its early stages.

The suspect did not resist when he was arrested by police who stormed the train after it was halted at Seubersdorf station. He had a bloodied knife on him.

A federal policewoman who happened to be on the train assisted the police efforts, while a doctor on board administered first aid to the injured before help arrived.

Around 420 police and other emergency service personnel were deployed to the scene.

The knife attack comes as Germany remains on high alert for terror attacks from Islamists and far-right extremists after a series of deadly incidents in recent years.

But an initial psychiatric assessment suggests the suspect was suffering from paranoid schizophrenia and was most likely not criminally responsible for his actions at the time, Nuremberg-Fuerth prosecutor Gerhard Neuhof said.

The Syrian told the psychiatric expert that for a while now he has "felt he was being followed by police" who wanted "to drive him crazy" and that he had attacked the first train passenger because he had imagined the passenger wanted to kill him.

The Syrian said the attacks that followed on other travellers happened "like in a dream", Neuhof said.

A judge on Sunday ordered the suspect to be admitted to a psychiatric hospital.

Prosecutors are accusing the suspect of attempted murder, attempted manslaughter and grievous bodily harm.

The Syrian arrived in Germany as a refugee in 2014. He was convicted in a minor fraud case last year, Nagel said.

He lost his job a day before the knife attack, she added.

Last May, a Syrian jihadist was given a life sentence for stabbing a German man to death and severely wounding his partner in a homophobic attack in the eastern city of Dresden.

In June, a Somali man fatally stabbed three women in the Bavarian city of Wuerzburg.