“The perpetrator is under control. Police measures are continuing,” Cologne police wrote on Twitter just after 3 pm after commandos had stormed the shop.

“A female hostage has been lightly wounded and is being cared for,” they added, calling on the public to keep their distance from the area.

The hostage taker also suffered injuries, a police spokesperson said, adding that the man's motives were not yet known.

Slightly after 4 p.m. police tweeted that the area around where the incident took place remains closed off.

Earlier Monday, eyewitnesses had reported hearing shots and possible smoke bombs being let off inside the massive station, which hosts many shops and cafes.

But police could not confirm any details as they rushed to evacuate the building.

Several heavily armed officers from a special response unit were seen immediately afterwards running across the Breslauer Platz square, on the opposite side of the tracks from the city's famous twin-spired cathedral.

Officers had later been in touch with the attacker to determine his demands and whether he was armed.

State rail operator Deutsche Bahn suspended all train traffic through Cologne, a major hub for rail travel through North Rhine-Westphalia state and nationwide.

Earlier the police also urged onlookers not to stream any videos at the scene and not to speculate. 

Police at the scene of Cologne Hauptbahnhof. Photo: DPA

The police also appealed on Twitter: “Please avoid this area.”

“Eye witnesses reported hearing shots, others spoke of smoke bombs, but we cannot confirm any of that so far,” a police spokesman told news channel NTV.

Cologne's Hauptbahnhof is one of the most important railway junctions on the Rhine, located in the city centre right next to the famous Cologne Cathedral, Germany's most visited attraction. Around 1,300 trains and up to 280,000 passengers pass through it every day on eleven tracks.