Police are hunting for the man pictured in the far right of this CCTV image of three suspected attackers
More than 30 people are believed to have been killed and dozens injured in attacks at Brussels international airport and a city metro station.
Twin blasts hit Zaventem airport at about 07:00 GMT, with 11 people reported killed.
Another explosion struck Maelbeek metro station near EU headquarters an hour later, leaving about 20 people dead.
Brussels police have issued a wanted notice for a man seen pushing a luggage trolley through the airport.
He was pictured in CCTV footage with two other suspects who are believed to have died in the blasts.
The Islamic State (IS) group said it was behind the attacks in a statement issued on the IS-linked Amaq agency.
Belgium has raised its terrorism alert to its highest level. Three days of national mourning have been declared.
Prime Minister Charles Michel called the latest attacks “blind, violent and cowardly”, adding: “This is a day of tragedy, a black day… I would like to call on everyone to show calmness and solidarity”.
‘The worst thing I’ve seen’
Two blasts tore through the departures area of Zaventem airport shortly after 08:00 local time (07:00 GMT).
A suicide bomber was “probably” involved, the Belgian prosecutor said.
Eleven people were killed and 81 wounded in the blasts, Belgian Health Minister Maggie de Block said.