Belgium is observing three days of mourning following bomb attacks in the capital Brussels that left 34 people dead and about 250 wounded.
A minute's silence for the victims will be held at midday (11:00 GMT).
Police are continuing a huge manhunt for a suspect caught on CCTV shortly before two bombs exploded at Zaventem airport on Tuesday morning.
An hour later another blast tore through a metro train near the Maelbeek station.
So-called Islamic State (IS) has said it was behind the attacks and warned that more would follow.
Meanwhile, the US state department has urged US citizens of the "potential risks" of travelling to Europe.
A statement said terror groups were planning "near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurants and transportation".
Tuesday's blasts came four days after the capture in Brussels of Salah Abdeslam who investigators say was involved in last November's terror attacks in Paris.
Abdeslam is due to appear before a pre-trial court in Brussels on Wednesday.
Hundreds of people crowded into Place de la Bourse late into Tuesday night, lighting candles and placing flowers in a vigil for the victims of the attacks.
Many cities around the world illuminated their landmarks in the colours of the Belgian flag in a show of solidarity.
Raids took place in Brussels and across Belgium on Tuesday as anti-terror police sought those linked to the attacks.
They issued a wanted notice for a man seen walking with two other suspects at the airport just before the blasts at a check-in hall.
He was pushing a luggage trolley with a suitcase thought to have contained a bomb that did not explode. The two other men are presumed to have died after detonating suicide devices.