Nine people have been injured in an attack on a bus in the northern German city of Luebeck, the interior minister for the state of Schleswig-Holstein said on Friday.

Hans-Joachim Grote said six people had suffered stab wounds and three others had received other injuries - including the driver, who was punched.

A police spokeswoman earlier told dpa three individuals had sustained serious injuries and five received minor wounds. Passengers reportedly overpowered the assailant.

German police said there was no indication that the attacker was politically radicalized.

"The identity of the perpetrator has been clarified: a 34-year-old German citizen resident in Luebeck," police added on Twitter.

Earlier, police in the state of Schleswig-Holstein, where Luebeck is located, tweeted that there was a major police deployment underway in the city.

"There is currently a major police deployment in Luebeck," the police force wrote. "We are examining the situation and will give more information later."

The packed bus was heading in the direction of Travemuende, a popular beach close to the city of Luebeck, when a man pulled a weapon on passengers, local media Luebecker Nachrichten reported, quoting an unnamed witness.