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The attack happened inside a supermarket on Fuhlsbüttler Street, as panicked shoppers fled the store to call for help. Hamburg Interior Minister Andy Grote told a news conference on Saturday that Friday's 26-year-old attacker was registered in intelligence systems as an Islamist but not as a jihadist, as there was no evidence to link him to an imminent attack. Mr Grote also said the attacker, a Palestinian asylum seeker who could not be deported as he lacked identification documents, was psychologically unstable. The Palestinian mission in Berlin had agreed to issue him with documents and he had agreed to leave Germany once these were ready, a process that takes a few months.

EXPRESS BREAKING NEWS: At least one dead in knife attack in Hamburg

Mr Grote said: "What we can say of the motive of the attacker at the moment is that on the one side there are indications that he acted based on religious Islamist motives, and on the other hand there are indications of psychological instability. "The attacker was known to security forces. There was information that he had been radicalised. "As far as we know ... there were no grounds to assess him as an immediate danger. He was a suspected Islamist and was recorded as such in the appropriate systems, not as a jihadist but as an Islamist." Prosecutors said the attacker pulled a 20-centimetre knife from a shelf at the supermarket and stabbed three people inside and four outside before passers-by threw chairs and other objects at him, allowing police to arrest him.

TWITTER Supermarket terror: One dead and several injured in Edeka supermarket

TWITTER Hamburg in terror: Armed officers swoop on supermarket after attacker leaves at least one dead

A 50-year-old man died of his injuries. None of the other six people injured in the attack is in a life-threatening condition. Hamburg’s own have-a-go heroes tackled the knifeman, police revealed. Witnesses described how the killer lunged at shoppers, stabbing at least three. Armed officers swooped in, locking down the area, as authorities described the incident as a "terror attack," the Bild reported. At 3.11pm fire fighters and police received dozens of emergency calls. The knifeman ran across the street after the attack in the Edeka supermarket, while armed units were scrambled.

#Barmbek: Ein Täter hat mehrere Personen in einem Supermarkt angegriffen & verletzt. Eine Person verstorben. Tatverdächtiger festgenommen. pic.twitter.com/TPKtqmjamp — Polizei Hamburg (@PolizeiHamburg) July 28, 2017

A manhunt for a second man was stood down after one arrest was made at the scene. Hamburg Police said there was just one attacker. The perpetrator was spotted in a police car, smeared with blood and “tied up”. Police caught him on an adjacent road to Hellbrookstraße near the scene.

REUTERS Armed police guard the supermarket in Hamburg, Germany

REUTERS Hamburg terror: Shoppers escorted from the area after one arrest

He was totally upset, waving his arms around as he left the supermarket Witness

An eyewitness said "n-tv": "I stood at the box when the culprit came back. He had a huge knife. “Smeared blood. He was totally upset, waving his arms around as he left the supermarket." The Fuhlsbüttler Straße was blocked off for several hundred metres with police tape. Policemen with machine guns were seen standing on the street.

BILD Police have surrounded a supermarket in Hamburg, Germany after an attack

AFP/Getty Images Police guard supermarket after knifeman kills one and wounds others

A police helicopter was circling overhead. Germany is on high alert since a spate of attacks on civilians last year, and a possible security lapse in a second deadly militant attack in less than a year, and two months before the general election, would be highly embarrassing for German intelligence, especially since security is a main theme in the Sept. 24 vote. A Tunisian failed asylum seeker killed 12 people by driving a truck into a Christmas market in Berlin in December, slipping through the net after intelligence officers who had monitored him reached the conclusion he was no threat.

REUTERS Crime scenes in Hamburg after at least one person killed by machete wielding attacker

GETTY/AFP The area has been placed in lockdown as emergency services assess the scene

BREAKING #Hamburg police arrest suspect after reported knife attack in which one person was killed in a supermarket, many injured.. #Germany pic.twitter.com/YL7fC9kBTL — Raveen Aujmaya (@raveenaujmaya) July 28, 2017