At least two shots were fired when police stormed the pharmacy.
Local media say the incident does not appear to have been terror-related.
Police quoted by the Koelner Stadt-Anzeiger daily said a couple were involved, and a man had argued with a woman in a McDonald's restaurant, before holding her in a pharmacy at the station.
Police tweeted that the hostage was slightly injured and was now being treated.
Beware of the message that will crash your PlayStation 4
Once the database rebuild is underway, it will scan the drive and create a new database of content installed on the system. According to users, a message containing a string of characters (or a specific one) has been shutting down the hardware.
The square and other areas surrounding the station were subsequently the scene of demonstrations against, and in favour of mass migration in response to the crimes. "We're doing everything to get the hostage out of there unharmed", police spokesman Christoph Gilles said initially.
German railroad operator Deutsche Bahn said that all train traffic was shut down.
NOAA maps show street-by-street views of Hurricane Michael's destruction
EDT, Michael was centered about 40 miles (65 kilometers) west of Columbia, South Carolina, with winds of 50 mph (85 kmh). But judging from the number of homes reduced to "sticks", he said "my sense is they are going to find more victims".
Police say officers have contact with the man and that trained hostage negotiators are working on the case.
"Police measures are continuing", Cologne police wrote on Twitter just after 3:00 pm (1300 GMT) after commandos had stormed the shop.
A second Royal Family member decides not to attend Princess Eugenie's wedding
Her elder sister Princess Beatrice , the maid of honour, will also deliver one of the readings, an extract from The Great Gatsby . Eugenie is following tradition by not revealing who designed her wedding gown, but she has said it will be a British designer.
Police forces stand at the Cologne, western Germany, main station Monday, Oct. 15, 2018, after they have closed parts of the station because of a hostage situation. No details have emerged yet about the hostage-taker or any potential motive.
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