Belgian news site RTL reported an operation was ongoing in the capital at Grand Place.
Police have blocked the streets in the Grote Markt area and do not allow to residents of the hotels and people of the restaurants to get on the street.
Police have reportedly asked also locals to move away from their windows.
One eyewitness described the scene, as euronews says:
“I was at a restaurant and the police asked us to finish our meals and to group together inside. They said to wait for their signal before leaving.”