The attacker, who has been arrested, carried out the attack as the bus was headed toward Travemuende, a popular beach near the city of Luebeck, local newspaper Luebecker Nachrichten reported.
Schleswig-Holstein's state interior minister, Hans-Joachim Grote, said his information was that nine people were injured - six with the knife, two passengers who fell and the driver, who was punched.
Contacted by Reuters, a police spokesman declined to give any details about the attacker or number of people injured, but said police were examining a backpack he may have been carrying.
The bus driver had immediately stopped the vehicle, allowing passengers to escape, while a police auto that happened to be close by arrived at the scene quickly, allowing officers to detain the assailant, the newspaper reported.
He is not believed to have been politically radicalised and there were no signs of a terrorist background, said officials. Police said authorities were still trying to determine the circumstances of and motive for the attack. Hingst said it wasn't clear whether it belonged to the suspect, but said there had been reports of smoke coming out of the backpack.
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"There are no indications that the man was in any way politically radicalized", Hingst said.
Video surveillance footage from the bus led to suspicion that he wanted to set fire to the vehicle, thereby injuring as many people as possible and potentially killing some.
A police patrol vehicle close to the horror in the Kucknitz district of Lubeck in northern Germany, was quick to the scene and the 34-year-old suspect was overpowered.
Police block the "Travemuender Landstrasse" street near the scene where a person had allegedly attacked passengers on a bus in Luebeck, Germany, 20 July 2018.