An axe-wielding attacker injured at least seven people at Dusseldorf station on Thursday night.
Witnesses described seeing a "crazed man" running through the busy station, striking commuters with an axe and leaving several wounded people lying on the floor surrounded by blood.
A suspect was arrested at the scene having attempted to escape by jumping off a nearby bridge and injuring himself.
Police had earlier said that other suspects could be on the run, but later revised the statement to say they were investigating whether any other people were involved in the attack.
The attack raised fears that terrorism had returned to Germany, less than three months after a lorry was driven into a Christmas market in Berlin, killing 12, in an attack claimed by the Islamic State of Iraq and the Levant group.
A German police spokesman said last night there were no indications the Dusseldorf attack was terrorism. "We are not using the words 'rampage' or 'terror'," the spokesman said.
The 36-year-old man, described by police as being from "the former Yugoslavia" and living in the nearby city of Wuppertal, suffered serious injuries and was being treated in a hospital.
"The suspect appears to have had psychological problems," police said.
Police said an axe was recovered and officers were searching the area in and around the station, which was closed for the investigation.
An earlier police statement that a second person had been arrested at the station was later withdrawn.
Footage showed terrified commuters fleeing the scene. One passenger, Bruno Macedo, was tweeting as the attack unfolded.
"Man with axe chased by police in Dusseldorf. Station closed . I am in the train things look bad," he wrote, adding: "Stay away from #Dusseldorf train station crazy man with #axe on the lose [sic]."
One witness described how she helped the 13-year-old victim. "She was obviously injured with the axe," she said, describing the "gaping wound" as like "someone had struck an axe in a tree".
"I helped her get the wound treated and called her father," the unnamed woman said.
Anti-terror police descended on the station in an "extensive operatrion", sealing off the perimeter of the station and preventing any trains from stopping. A helicopter circled overhead.
The arrested suspect reportedly ran towards a nearby underground station and jumped from a bridge in an attempt to flee police. However, he was arrested after seriously injuring himself in the escape attempt.
Rainer Kerstiens, a police spokesman, said last night that more suspected attackers were believed to be on the run, but a second spokesman said there was no serious threat of further attacks.
German authorities have heightened security measures following a series of attacks in public places over the past year.
Aside from the Berlin Christmas market attack, Isil claimed two attacks in Germany in late July - on a train near Wuerzburg and on a music festival in Ansbach - in which asylum-seekers wounded 20 people in total.
In addition, nine people were shot and killed in an attack in a shopping centre in Munich in July. The killer was an 18-year-old German-Iranian who had been in psychiatric treatment and was obsessed with mass killings.