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The perpetrator is thought to still be on the run, police said, while the motive remains unclear.

Police cordoned off the B level of the Hauptwache station in the major city.

While chilling pictures of the blood splattered platform emerged on Twitter.

(Image: TWITTER) (Image: TWITTER)

Frankfurt police tweeted: "There was a knife assault at the #Hauptwache in #Frankfurt.

"That’s why so many colleagues [police officers] and rescue workers there."

They added: "We are asking you to refrain from speculation... You are scaring your fellow citizens. There is no danger."

It is thought the incident involved four teens aged between 16 and 18 and started at 17.40pm (local time).

It comes as Europe is on tenterhooks after several countries – including Britain – ramped up their terror alert level.

Germany has been rocked by violence in the past few months.

On July 18 a teenager posing as an Afghan refugee went on a bloody rampage on a train, hacking at passengers and wounding five.

Just four days later a mentally unstable teen shot dead nine people in a shopping centre before taking his own life.

On July 24 a man posing as a Syrian refugee hacked a pregnant woman to death.

(Image: TWITTER/@HUSSEDOGRO)

The alleged ISIS fanatic wounded 15 and killed himself in the attack on a music festival.

The UK is on the second from the highest level, "serious", which means a terrorist attack is likely.