Police said that the incident happened at around 2.30 pm on Appelhofplatz. The horses were pulling a coach belonging to the Treue Husaren.
At this stage reports on the number of injured people vary. Police have confirmed that several people were injured.
#PolizeiNRW #Köln #Leverkusen : The Rose-Monday parade is currently stopped at the square Appelhofplatz. According to provisional information, the horses were spooked at the site. Several persons injured. Emergency services on the scene. News soon. #Karneval2018 #Rosenmontag pic.twitter.com/fb4tgNKsnp— Polizei NRW K (@polizei_nrw_k) February 12, 2018
The Kölner Stadt Anzeiger reports that four people were injured, According to its report, one woman was run over by the coach and had to be brought to hospital.
Broadcaster ARD reports that crowds at the site of the accident were "shocked and aggressive." There were several emergency service vehicles at the scene.
The parade was temporarily stopped, but authorities announced shortly before 3.30 pm that proceedings had commenced once again.
According to the Rheinische Post there have been fierce arguments in recent years over whether horses should be allowed at the parade, which is the biggest in Germany and attracts over a million spectators.
There have been several accidents involving horses in the past and the Cologne Carnival Committee recently tightened the rules for how horses can be used.