Riots broke out in several Belgian and Dutch cities after Morocco's 2-0 upset win over Belgium at the World Cup on Sunday.
Police detained about a dozen people after using water cannon and tear gas to disperse crowds in Brussels and eight more in the Northern city of Antwerp.
Two police officials were injured in the Dutch port city of Rotterdam. By late on Sunday evening, an uneasy calm had returned to most of the cities involved.
Dozens of rioters overturned and torched cars, set electric scooters on fire and pelted cars with bricks. Police moved in after one person suffered facial injuries, Brussels police said.
"The rioters used pyrotechnic material, projectiles, sticks, and set fire on the public highway," the police said.
"Also, a journalist was injured in the face by fireworks. It is for these reasons that it was decided to proceed with a police intervention, with the deployment of water cannon and the use of tear gas."
Philippe Close, the mayor of Brussels, urged people to stay away from the city center and said authorities were doing their utmost to keep order in the streets. Even subway and tram traffic had to be interrupted on police orders.
"Those are not fans, they are rioters. Moroccan fans are there to celebrate," Close said.
There were also disturbances in the city of Antwerp and Liege.
"Sad to see how a few individuals abuse a situation to run amok," said Interior Minister Annelies Verlinden.
Police in the neighboring Netherlands said violence erupted in the port city of Rotterdam, with riot officers attempting to break up a group of 500 football fans who pelted police with fireworks and glass.
Media reported unrest in the capital Amsterdam and The Hague.
Morocco's victory was a major upset at the World Cup and was enthusiastically celebrated by fans with Moroccan immigrant roots in many Belgian and Dutch cities.