According to Spiegel newspaper, special forces have shut down the whole street in front of a building near the Cologne Cathedral, which is being searched at the moment.
At the same time, the newspaper reported that an armed suspect was detained shortly after near Breslauer Platz metro station.
According to eyewitnesses, a man and a woman fled the scene in a car, while another suspect walked to the bank of the river Rhine. A police spokesman said later that the shooting could be related to biker gangs.