Two police officers on motorbike were then obliged to carry out a manoeuvre and crashed into each other. Both officers were taken to hospital suffering from light injuries.
The prime minister's spokesman says that the incident was a regrettable one and that there was no intent to harm.
PM Michel and Theresa May were at the Saint-Symphorien military cemetery in Mons to mark the centenary of the Armistice that ended the Great War. After the ceremony they set out for SHAPE, the central command of allied forces in Europe. Around 10:40 an incident occurred when a vehicle belonging to a member of the public ended up in the convoy.
PM Michel, who is an enthusiastic motor biker, stopped the motorcade and stepped out of his car. Theresa May remained seated in hers. Neither the Belgian or British leader were hurt. A federal police spokesman told reporters later that the officers would soon be able to leave hospital.