An international manhunt has been launched for one of the terrorist suspects behind co-ordinated bombings in Brussels which left 34 dead and almost 200 - including two Britons - injured.
A series of police raids were mounted across Belgium, leading to the discovery of an explosive device containing nails, chemical products and an Islamic State (IS) flag, almost 12 hours after the first explosion, at around 7am (GMT). The terror group has claimed responsibility for the attacks.
King Philippe of Belgium led the calls for calm as Belgian police issued an image of the fugitive, one of three seen pushing luggage trolleys through Zaventem airport moments before two bombs exploded.
A third bomb was deactivated at the airport hours after the initial attack - which was followed by a bomb blast on a Metro train in the city centre as terrorists inflicted a new outrage on a European capital.
Prosecutor Frederic Van Leeuw said the forensic operation would last well into the evening.
He said: "A photo of three suspects was taken at Brussels airport.
"Two of them have probably committed a suicide attack, the third - dressed in a white jacket and wearing a hat - is actively sought.
"Various departments and experts are currently in various crime scenes. This will take place for many hours to come.
"Due to the violence of the attacks, this investigation is particularly difficult.
"Various operations are ongoing across the country and several witnesses have been heard.
"Several explosions have been heard. They are due to bomb squad activity upon the discovery that the suspects might have left explosives behind. And this could continue."
The attacks left a major city in lockdown once again less than five months after Paris was hit by a wave of deadly strikes.
The atrocities on Tuesday, condemned as "blind, violent and cowardly" by Belgian prime minister Charles Michel, came after the arrest last week of terror mastermind Salah Abdeslam, who plotted November's massacre in the French capital.
Security was being stepped up at major transport hubs around the continent, with British police forces boosting numbers at "key locations" including ports, airports and the rail network.
French prime minister Manuel Valls said: "We are at war. In Europe we have been subjected to acts of war for several months."
As the city went into lockdown:
:: Local media reported that 20 people were killed following the blast at Maelbeek metro station, while 14 died in the suicide attack at the airport
:: The number of people injured in both attacks was believed to be 198
:: Two Kalashnikov rifles and an unexploded bomb belt were found at the airport
:: The Foreign Office said two British nationals are known to have been injured
In a televised address, King Philippe said he and Queen Mathilde "share the pain" of all those who had suffered in the attacks.
But he called on Belgians to stay "confident" in the face of terror.
He said: "Today our country is in mourning. For each of us this March 22 will never be a day like any other.
"In the face of threats, we will continue to respond together, firmly, with calm and dignity."
As night fell on Brussels, Mr Michel lit a candle at a vigil at Place de la Bourse, the city's stock exchange building.
He told a press conference earlier that the atrocities had killed people whose lives "were in full course".
He said: "The lives of people who were most likely travelling without a care in the world, going to work or to school, lives that have been broken by extremism."
Witnesses reported the chaos that descended on the transport hubs as the terrorists struck.
Jef Versele, 40, from Ghent, told the Press Association: "I was on my way to check in and two bombs went off - two explosions.
"Everything was coming down. Glassware. It was chaos. It was unbelievable. It was the worst thing."
Footage from inside the airport building showed a scene of devastation with ceiling tiles strewn across the floor and suitcases abandoned.
Images of passengers climbing from a train into a smoke-filled tunnel near Maelbeek station were reminiscent of scenes following the July 7 attacks in London.
Other images showed the injured from the Metro being treated in the street, while at the airport people could be seen fleeing in terror in video footage shot from an airport car park.
International leaders united in support for Belgium, with David Cameron branding the atrocities "appalling" and US president Barack Obama condemning the "outrageous attacks against innocent people".
The Prime Minister's official spokeswoman said Britain was also sending a team of specialist police officers to the city to assist with the investigation.
And the Foreign Office updated its travel advice to Belgium, advising against travel to Brussels.