Belgian police were on Wednesday raiding properties in the capital, Brussels, following bomb attacks at the main airport and a metro station, killing 31 and injuring hundreds.
The police issued a wanted notice for a suspect thought to be involved in the twin explosions which tore through Zaventem airport.
He was seen on CCTV pushing a trolley through the airport with two other suspects. Both those men are believed to have died in the blasts, possibly by detonating suicide devices.
So-called Islamic State (IS) said it was behind both the attacks in the Belgian capital on Tuesday night (Australasia time).
Belgian health minister Maggie De Block spoke, on Wednesday morning (Australasia time), to Belgian broadcaster VTM and said there were 250 injured in the blasts and 31 dead.
Eleven people are thought to have died at Zaventem Airport in Brussels and 20 at the Maalbeek metro station, near the European Union headquarters.

Belgian news organisation RTBF spoke with Christian Delhasse, who was driving the train that came under attack in Maelbeek: “It was 9.15am when the bomb went off. We are on lines 1-5, and the train starts up again towards Arts-Loi when the bomb went off. The conductor immediately stopped his train and its three carriages, thinking at first that it was a technical problem.”
He quickly realised however that it was much worse and went to check on his passengers: “I did what I had to do,” Delhasse told RTBF. “Nothing happened to me, not a single wound. I immediately followed the protocols, that’s all I can say.”
“This is a day of tragedy, a black day,” Belgian Prime Minister Charles Michel said. “I would like to call on everyone to show calmness and solidarity.”
We will defend and protect our values and freedom. We are confronted with a barbaric enemy. But we are determined and united.
— Charles Michel (@CharlesMichel) March 22, 2016
Belgium has raised its terrorism alert to its highest level. Three days of national mourning have been declared. Leaders from around the world have united against the attacks in Belgium.
"The thoughts and prayers of the American people are with the people of Belgium" —@POTUS on the attacks in #Brussels https://t.co/TWxnIDfDqL
— White House Archived (@ObamaWhiteHouse) March 22, 2016
I have just spoken to the Belgian PM and offered our sympathies and condolences. We must stand with Belgium at this very difficult time.
— David Cameron (@David_Cameron) March 22, 2016