Belgian Prime Minister Charles Michel says Brussels has been placed on its highest level of terror alert in response to information about the risk of an attack like the one in Paris last week.
Mr Michel said the fear was that "several individuals with arms and explosives could launch an attack, in several places".
Some of the attackers who killed 130 people in Paris lived in Brussels - the leading suspect Salah Abdeslam is believed to have gone back to Belgium.
He is now the focus of a huge manhunt.
As a result, the Brussels metro is closed until Sunday and people have been told to avoid crowds.
Global Radio News reporter in Brussels Georg Von Harrach says the city is extremely quiet;
