Belgian Prime Minister Charles Michel has said that the decision to put the capital Brussels on high alert is linked to an imminent threat of terror attacks.
According to News.com.au, Brussels shut its metro system on Saturday, cancelling all public events as one of the Paris attack gunmen is still on the run.
The residents were urged to stay indoors and away from crowded areas.
Authorities are on the hunt for Salah Abdeslam, 26, who is said to have been the "eighth attacker" in the Paris carnage.
Abdeslam is believed to be from the Brussels neighbourhood of Molenbeek and fled back to Belgium just hours after the Paris attacks.