Dortmund police have said the level of violence between rival Borussia Dortmund and Schalke 04 fans on Saturday was the worst in years as nearly 200 arrests were made for the Ruhr derby.
Schalke claimed a 2-1 win at neighbours and defending Bundesliga champions Borussia on Saturday, but the victory was over-shadowed by violent clashes in Dortmund between fans and police with eight officers injured.
A total of 180 football fans were arrested, 163 from Schalke and 17 from Dortmund, and police report fireworks, pepper spray, reinforced gloves and other weapons were all seized.
The organised violence is of obvious concern ahead of Wednesday's Champions League group game between Real Madrid and the German champions in Dortmund.
"The level of violence was much more severe than in previous years," Manfred Radecke from the Dortmund police told SID, an AFP subsidiary, with the German Football Federation (DFB) almost certain to investigate the rioting.
"We have to plan for riots and deploy the correct number of officers and put a plan in place.
"But we hadn't expected that things would degenerate to such an extent and that we would need to use a water cannon and tear gas."
Police used tear gas to break up the melee when a 600-strong group of Schalke fans was attacked by masked Dortmund supporters on their way to the Signal Iduna Park stadium.
A water cannon was also used to prevent Schalke fans tearing down a fence near the stadium, while a restaurant near the ground was ransacked with Dortmund fans using the broken furnishings as weapons.
Fans also tore up paving stones to use "as missiles against opposing fans and police officers".
"We don't regard these people as football fans," added Radecke.
"They use every opportunity to play out their aggression.
"If police have to step in, they happy to target them as well."
An Under-17 match between Schalke and Dortmund took place on Sunday with a large increase in police numbers.