A woman has been arrested after 17 people were injured in a horror train station knife rampage in Hamburg - with four victims now fighting for their lives. 

Police confirmed they had arrested a 39-year-old female suspect in connection with the stabbing spree at Hamburg Central Station on Friday afternoon.

The suspect is believed to have acted alone and there was no sign they had a political motive, police said. 

Officers 'approached her, and the woman allowed herself to be arrested without resistance', Hamburg Police spokesman Florian Abbenseth told journalists in comments carried by public broadcaster ARD.

'We have no evidence so far that the woman may had a political motive,' Abbenseth said. 

'Rather, we have information based on which we now want to investigate whether she may have been experiencing a psychological emergency.'

At least 17 people were injured in the attack in Germany's second-biggest city, a spokesman for the Hamburg fire department told AFP. Four of them had suffered life-threatening injuries, the spokesman added, revising down an initial figure of six.

Six others are severely injured and seven more suffered light injuries, the spokesman for the fire department said.

The suspect targeted people on the platform between tracks 13 and 14 in the station, according to police.

Footage posted on social media appeared to show a woman, wearing a hoodie and tracksuit bottoms, being arrested and led away by police officers.

The force said they were not seeking other suspects and there was no immediate information on a possible motive.

The station in downtown Hamburg is a major hub for local, regional and long-distance trains. 

The Hamburg police reported a 'major police operation' on X.

'There is currently a major police operation in #Hamburg on #Hauptbahnhof!

'We are investigating the background and will provide further information here shortly,' the force added.

Pictures on social media showed crowds gathered outside the transport hub, as emergency service vehicles and forensics swarmed the scene.

According to German newspaper Bild, some of the injured were being treated on trains.

In one image a man was being treated on the platform, while another was taken away on a stretcher.

A young woman at the station witnessed the stabbing. She told Hamburger Abendblatt: 'Luckily I didn't have headphones on, so I heard everyone screaming, and then they all ran away.' 

In a statement, the national railway company Deutsche Bahn said it was 'deeply shocked' by the attack. 'Our thoughts and condolences go out to the injured.' 

Regional public broadcaster NDR reported that the attack took place shortly after 6 pm (5pm GMT) in front of a waiting train. 

A high-speed ICE train with its doors open could be seen at the platform after the attack.

Railway operator Deutsche Bahn said it was 'deeply shocked' by the attack.

Four tracks at the station were closed Friday evening, and some long-distance trains were delayed or diverted.

Carrying weapons, including knives, is banned at the station and on local transport in Hamburg.