The evacuation in the Old Town and Deutz neighbourhoods began with officials going door to door to tell people they must leave their homes.
Many of the city’s usually bustling streets were eerily deserted as shops, restaurants and businesses were told to stop operating during the day.
Cultural institutions including the Philharmonic Hall and many museums were also affected, as well as government buildings, 58 hotels, and nine schools.
Transport was severely disrupted, with all roads closed in the area, many trains cancelled and the Messe/Deutz train station was closed from 08:00 local time (07:00BST).
The authorities had set up two drop-in centres for people who did not have anywhere to go during the evacuation period.
Residents were told to “stay calm”, bring their ID and any essential medications, and to take care of their pets.
For some people, the evacuation was more than a little inconvenient.
Fifteen couples were scheduled to get married at Cologne’s historic town hall but the ceremonies were relocated to a location in another part of the city, local media reported.
