30 masked people armed with knives stormed a bar on Place Mansart in the Wallonian city of La Louvière on Saturday evening.
They broke and vandalised everything in the establishment according to witnesses, before quickly leaving. One customer was injured during the incident, his life is not in danger.
Witnesses reported that that the perpetrators told customers at the bar to "relax" and that they are "not there for them."
The cars which the perpetrators left with appear to have carried French licence plates. Surveillance videos are yet to be analysed by police, who are investigating the matter.
The bar has been closed in the meantime by the mayor of La Louvière.