Belgium has raised its terror alert in the Brussels region to the highest level, warning of a “very serious” and “imminent” threat.
The metro will be closed till at least Sunday, and the public has been warned to avoid crowds, including shopping centres and concerts, a statement said.
The warning for the rest of Belgium stays at a lower level – still serious.
Brussels was home to the suspected perpetrators of the Paris terror attacks carried out a week ago.
One of those being sought, Salah Abdeslam, is believed to have gone back to Belgium.
On Friday, the UN Security Council unanimously adopted a resolution to “redouble” action against Islamic State following last week’s deadly attacks in the French capital in which 130 people died.
The French-drafted document urges UN members to “take all necessary measures” in the fight against IS, which said it carried out the attacks.