Police said the suspect was still at large and have warned people to stay indoors until he is captured.
They tweeted: “Warning: Avoid Rosenheimer Platz. Perpetrators are still volatile. Residents please stay in the houses Munich.
“We are searching for the offender with all police officers available.
“Until now we know nothing about the motivation.”
They described the attacker as a man in his 40s who fled the scene on a black bicycle.
They said: “He is wearing a green training jacket, is riding a black bike. He also had a backpack with camping mat.”
Police have warned members of the public not to approach the man but to contact the emergency services if they see him.
The man launched the attack at Rosenheimer Platz underground station which is on the trunk line of the Munich S-Bahn.
Several people have reportedly been stabbed but their injures are not said to be life-threatening at this stage.
Images from the sene show a number of ambulances parked outside the station and a police helicopter hovering above the scene.
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