Eight people are reported to have been injured after a man armed with a knife attacked passengers on a bus in the northern German city of Luebeck.

The suspect was overpowered and arrested after the incident on the busy service north-east of Hamburg, near the Baltic coast.

Details of what exactly happened are sketchy, and authorities had no immediate information on the assailant’s motive.

The scene of the attackA view of the bus where the attack took place (AP)

A spokeswoman for prosecutors, Ulla Hingst, told n-tv television that the bus driver stopped the vehicle and let the passengers out after the attack. She said the weapon that the assailant apparently used was a knife, although that is still under investigation.

Experts were also examining a backpack on the bus as a precaution.

Ms Hingst said it was not clear whether the luggage belonged to the suspect, but said there had been reports of smoke coming out of the backpack.

She said the identity of the suspect, who was being questioned by police, has yet to be confirmed.

Local officials at the sceneHans-Joachim Grote, left, an interior minister for Schleswig-Holstein, and Jan Lindenau, mayor of Luebeck, at the scene (AP)

“The background to this act is completely unclear,” she said.

“We are investigating in all directions. We cannot currently rule anything out.”

German news agency dpa quoted police as saying that three people received “medium-serious” injuries in the incident, while five others received minor injuries.

Ms Hingst said the total number of injuries was not clear, but said there was one serious injury.