Police used water cannon and teargas after coming under attack from football supporters who brought havoc to the centre of Brussels on Sunday following Morocco's shock 2-0 World Cup win over Belgium in Qatar.
Dozens of fans smashed shop windows, threw fireworks and torched vehicles.
Even before the end of the match, "dozens of people, including some wearing hoodies, sought confrontation with the police, which compromised public safety," Brussels police said in a statement.
A spokeswoman said some fans were armed with sticks and a journalist "was injured in the face by fireworks".
Around a hundred police officers were mobilised while residents were warned to avoid certain areas of the city centre. Metro stations were closed and streets blocked to limit the spread of the violence.
"I condemn in the strongest terms the incidents of this afternoon. The police have already firmly intervened. I therefore advise against fans coming to the city centre. The police are doing all they can to maintain public order," tweeted the mayor of Brussels, Philippe Close.
"I have ordered the police to carry out arrests of the troublemakers."