Hundreds of fans set cars on fire and injured 22 police officers.
Police trucks fired water cannons at crowds gathered in front of the city’s stock exchange in attempts to disperse them.
Brussels police said some 1,500 people had come to celebrate Morocco’s 2-nil win over Ivory Coast, but some of them started to behave violently and attacked police officers and firemen.
Morocco scored 2 goals in the space of 5 minutes to seal their place in the finals, where their last appearance was in France in 1998.
At the last count, 29 teams have made it through to the 2018 FIFA World Cup.
Five from Africa, 13 from Europe, four from South America, another four from Asia and three from North and Central America.