Brussels (AFP) - Belgium launched a huge manhunt Tuesday after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe.
Two massive suicide blasts by attackers with bombs in their bags hit the check-in hall at Zaventem Airport, strewing the scene with blood and mangled bodies and sending hundreds of terrified travellers fleeing in terror.
Belgian authorities released pictures of two of the suspected attackers pushing trolleys with their bombs through the terminal and said they were "actively searching" for a third whose bomb failed to go off.
Police helicopters hovered over the city late into the night and raids were under way across Belgium, prosecutors said, adding that a bomb, an Islamic State flag and chemicals had been found in one apartment.
The fact that extremists were able to hit high-profile targets in Brussels, Europe's symbolic capital, just months after IS militants killed 130 people in Paris, will raise fresh questions about the continent's ability to cope with the terror threat.
It also underscores doubts about how Belgium has allowed extremism to develop unchecked, coming just four days after the arrest in Brussels of key Paris suspect Salah Abdeslam after four months on the run.
"This is a day of tragedy, a black day," Belgian Prime Minister Charles Michel, announcing three days of national mourning after the "deadliest attacks we have ever seen in Belgium".
Belgian King Philippe condemned the "cowardly and odious" assault.
The Islamic State claimed the bombings, saying "soldiers of the caliphate" had carried out the attacks against "the crusader state" of Belgium.
- 'Extreme barbarity' -
Leaders across Europe reacted with outrage, with the EU vowing to combat terrorism "with all means necessary" on a continent that has been on high alert for months.
"The whole of Europe has been hit," said French President Francois Hollande, whose country is still reeling from November's attacks.
Several global landmarks including Paris' Eiffel Tower and Berlin's Brandenburg Gate, as well as the European Commission in Brussels, were illuminated in the colours of the Belgian flag -- black, yellow and red.
Hundreds of flights and trains were cancelled Tuesday as security across Europe was tightened after the bombings, which Michel branded "blind, violent and cowardly".
But as Belgium raised its terror alert to the maximum level four, he insisted that Belgium would not be cowed.
"People were just going to work, to school and they have been cut down by the most extreme barbarity," Michel told a news conference. "We will continue to protect liberty, our way of life."
About an hour after the airport blasts at around 8:00 am (0700 GMT), a third explosion rocked Maalbeek metro station, in the heart of the city's EU quarter, just as commuters were making their way to work.
The city is the headquarters of both NATO and the European Union.
Belgian authorities published surveillance camera images showing the three male suspects of the airport attack-- two have dark hair and were both wearing a glove on only one hand, and a third, being hunted by Belgian police, is wearing a hat and a white coat.
"They came in a taxi with their suitcases, their bombs were in their bags," Zaventem mayor Francis Vermeiren said. "They put their suitcases on trolleys, the first two bombs exploded. The third also put his on a trolley but he must have panicked, it didn't explode."
Belgian authorities had been on alert after Abdeslam, Europe's most wanted man, told investigators he had been planning an attack on Brussels.
Pierre Meys, spokesman for the Brussels fire brigade, told AFP at least 14 people had been killed at the airport, while Brussels mayor Yvan Mayeur said "around 20" died in the metro.
Witnesses described horrific scenes at the airport, with victims lying in pools of blood, their limbs blown off.
- Chaotic scenes -
There were chaotic scenes as passengers fled in panic, and plumes of dark smoke could be seen rising from holes punched through the roof of the building by the blasts.
"A man shouted a few words in Arabic and then I heard a huge blast," airport baggage security officer Alphonse Lyoura told AFP, his hands bloodied.
"A lot of people lost limbs. One man had lost both legs and there was a policeman with a totally mangled leg."
At Maalbeek station, paramedics tended to commuters with bloodied faces as the city's normally peaceful streets filled with the wailing of sirens.
The wounded in the two attacks included four US Mormon missionaries, two Britons, eight French and two Colombians.
Airports across Europe swiftly boosted security, while across the Atlantic, New York and Washington ordered security personnel to key areas.
Messages of solidarity poured out on social media, with thousands of people sharing images of beloved Belgian cartoon character Tintin in tears.
Brussels residents held a candlelit vigil in the Place de la Bourse square where they sang songs and waved the Belgian flag.
US President Barack Obama said Washington stood with Belgium in the face of the "outrageous" attacks and ordered US flags flown at half mast, while UN chief Ban Ki-moon said those responsible for the "despicable" bombings" should face justice.
It has been a week of drama in Brussels. Last Tuesday saw a shootout in the city's south that saw an Algerian IS-linked militant killed.
Investigators believe Abdeslam slipped out of the apartment as the gunbattle erupted. He was arrested three days later in Brussels' gritty Molenbeek district -- just around the corner from his family home.
Foreign Minister Didier Reynders said at the weekend that Abdeslam -- believed to have played a key logistical role in the Paris carnage -- had told investigators he was planning some sort of new attack in Brussels.
Belgian police also named a new suspect -- Najim Laachraoui -- whose DNA was found on explosives used in the Paris attacks.