The number of victims of a knife attack at a German train station rises to 18.

At least 18 people were injured in a knife attack at Hamburg station on Friday night, German newspaper Bild reported, and local police confirmed they had arrested the attacker.

Four of the victims are in critical condition and six others are seriously injured, Bild reported, adding that the motive for the attack was unclear.

The alleged attacker, a 39-year-old woman, was arrested "without resistance," police said, ruling out a political motivation.

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"So far, we have no indication that the woman may have acted out of political motives," Florian Abbenseth, a spokesman for the armed forces, told ARD.

Police are investigating the possibility that the detained suspect suffered a "psychiatric emergency," he continued.

The woman, a German national, "acted alone" at this station in Germany's second most populous city, Hamburg police said in X.

Rather, we have findings based on which we are investigating whether he may have been in a state of mental distress," he added.

Some of the victims were being treated on trains , according to the German newspaper Bild.

The head of the German government, conservative Friedrich Merz, said he was "shocked" by this act of violence.

Germany has been rocked in recent months by a series of violent attacks motivated by jihadists and far-right extremists, bringing security issues to the forefront.

Last weekend, four people were injured in a stabbing attack in Bielefeld, in the west of the country. The alleged perpetrator is a 35-year-old Syrian man, who has been detained by authorities, who suspect him of an Islamist attack.

With information from AFP and Reuters.