An axe attack at the main railway station in Dusseldorf last night left seven people injured, according to reports.
German police said they had detained a man involved at the city’s central train station.
The attack happened at about 9pm local time.
The 36-year-old suspect from the former Yugoslavia suffers from psychological problems, police said.
They said the assailant “attacked people at random”.
No fatalities were reported but three people were seriously injured. The attacker was also badly injured after jumping from a bridge while trying to escape.
Rail services were halted as a large number of police were deployed to search the area for possible further suspects.
The motive for the attack is unclear, and police are not describing it as being related to terrorism.
German federal police earlier tweeted a warning to the public not to engage in speculation.
Germany is on high alert for terror attacks. A jihadist drove a lorry into crowds at a Christmas market in Berlin in December, killing 12 people.