One person is dead and four others injured after a knife attack in a supermarket in the German city of Hamburg.

The motive for the attack is not yet known and terrorism has not been ruled out.

A video obtained by Euronews showed the attacker subdued on the ground, apparently after being restrained by passersby.

A witness told Euronews that he saw six or seven men, some wielding chairs, chase the man down the street.

He said: “I was in my car and all of a sudden there was a young man aged about 30 just a few metres away from me. He had a knife in his hand, I could see blood on the knife. I was so shocked.

“And behind him, there were six or seven men wielding chairs, trying to stop him. At one stage I saw them hit the suspect with the chairs.

“At first I didn’t know what was going on. I thought it was just an argument, because that happens a lot here. But afterwards when I learnt what happened it was terrifying.”

Police say they believe the assailant acted alone.

Germany has been on high alert for terrorist attacks for months.