One person has been killed and several injured in a knife attack in a Hamburg supermarket, German police say.
"An offender has attacked and injured several people in a supermarket".
Germany is on high alert following a series of terror attacks in the country previous year.
The assailant was placed under arrest, police said, adding that it was too soon to speculate a motive.
"He struck out at customers without warning", Heike Uhde, a police spokeswoman said.
Two eyewitnesses to the attack said the man shouted "Allahu Akbar" but police said they were unable to confirm the reports.
"Initial reports about robbery as a possible motive so far have not been confirmed", police said. Bystanders followed the suspect and alerted the police, who arrested the man shortly thereafter in a nearby street. Photos and videos showed a large number of emergency services, including a helicopter and heavily-armed police officers, at the scene.
The stabbing happened Friday afternoon local time at a supermarket in the Barmbek area to the north of the city.