Police have announced a "major operation" and closed a road running between two central locations in the city.
An explosion has occurred in the centre of the German city of Cologne, according to media outlets.
It happened early on Monday morning at around 5:50 am local time, reportedly injuring two people so far, including a cleaner who was seriously wounded.
Police in the western North Rhine-Westphalia region initially cordoned off a major area in Hohenzollernring — Cologne's main entertainment district — between the Rudolfplatz and Friesenplatz metro stations before lifting the barriers, according to a post on X.
The police did not provide any information about the cause of the explosion, which took place outside the entrance of a nightclub in an area popular for its nightlife.
A spokesman for the police reported on local television that the explosion could have harmed more people if it had occurred later in the day.
Photos posted to social media show several glass windows burst and ceiling panels hanging from overhead outside the Vanity nightclub, which opened in 2011.