Police said the motive behind the attack is still not known.

A large number of people were also injured in the incident.

Police said they found a dead person at the scene who they believe may have been a perpetrator and investigations are continuing, reports BBC.

Hamburg's Interior Minister, Andy Grote, said on Twitter that police special forces and a large number of officers had been deployed to the scene.

What is  Jehovah's Witnesses?

Jehovah's Witnesses is a millenarian restorationist Christian denomination with nontrinitarian beliefs distinct from mainstream Christianity.

Jehovah's Witnesses are directed by the Governing Body of Jehovah's Witnesses, a group of elders in Warwick, New York, United States, which establishes all doctrines based on its interpretations of the Bible.