German police conducted a raid on Tuesday in connection to a suspected Islamist who took a woman hostage inside Cologne's main train station pharmacy the day before.

Police, who have yet to officially state whether the incident was a terrorist act and have not definitively identified the suspect, declined to name the time and place of the raid.

In a Twitter post, police called on the public to submit photos and video footage of the hostage-taking, adding that investigations into the incident were "running at full speed."

Rail operator Deutsche Bahn said that train travel to and from the station was once again running as normal. Tens of thousands of people were affected by the closure of the station on Monday.

The hostage-taker - armed with camping gas cartridges and fire accelerants - was shot when police moved in on the pharmacy where he was holding a woman hostage and later had to be reanimated.

A police spokesman said Tuesday that he remained in hospital in critical condition.

The incident began around midday on Monday when the assailant lit a Molotov cocktail in a fast food restaurant in the station, injuring a 14-year-old girl. One other person was injured in the restaurant and a third person suffered shock.

The assailant ran out when the sprinkler system was activated, seeking refuge in the pharmacy and taking the woman hostage.

Police cited witnesses as saying that the perpetrator had claimed to be a member of the Islamic State group, but said that this had not been independently verified.

Police have yet to formally identify the suspect. They said late Monday that identity documents belonging to a 55-year-old Syrian man had been found at the scene and "probably" belonged to the assailant.