Thirty-four people were killed in attacks on Brussels airport and a rush-hour metro train in the Belgian capital on Tuesday, according to public broadcaster VRT, triggering security alerts across Europe and bringing some cross-border traffic to a halt.
A witness said he heard shouts in Arabic and shots shortly before two blasts struck a packed airport departure lounge at Brussels airport. The federal prosecutor said one of the explosions was probably triggered by a suicide bomber.
The blasts occurred four days after the arrest in Brussels of a suspected participant in November militant attacks in Paris that killed 130 people. Belgian police and combat troops on the streets had been on alert for reprisal but the attacks took place in crowded areas where people and bags are not searched.
All public transport in Brussels was shut down, as it was in London during 2005 Islamist militant attacks there that killed 52. Authorities appealed to citizens not to use overloaded telephone networks, extra troops were sent into the city and the Belgian Crisis Centre, clearly wary of a further incident, appealed to the population: "Stay where you are".
British Sky News television's Alex Rossi, at the airport, said he heard two "very, very loud explosions".
"I could feel the building move. There was also dust and smoke as well...I went towards where the explosion came from and there were people coming out looking very dazed and shocked."
VRT said police had found a Kalashnikov assault rifle next to the body of an attacker at the airport. Such weapons have become a trademark of Islamic State-inspired attacks in Europe, notably in Belgium and France, including on Nov. 13 in Paris.
An unused explosive belt was also found in the area, the public broadcaster said. Police were continuing to scour the airport for any further bombs or attackers.
Alphonse Youla, 40, who works at the airport, told Reuters he heard a man shouting out in Arabic before the first explosion. "Then the glass ceiling of the airport collapsed."
"I helped carry out five people dead, their legs destroyed," he said, his hands covered in blood.
A witness said the blasts occurred at a check-in desk.
Video showed devastation in the hall with ceiling tiles and glass scattered across the floor. Some passengers emerged from the terminal with blood spattered over their clothes. Smoke rose from the building through shattered windows and passengers fled down a slipway, some still hauling their bags.
VRT said 20 were killed in the metro train and 14 at the airport. Authorities had earlier put the toll at 11 in the airport bombing and 15 in the underground train.
Many of the dead and wounded at the airport were badly injured in the legs, one airport worker told Reuters, suggesting at least one bomb in a bag on the floor.
Britain, Germany, France and the Netherlands, all wary of spillover from conflict in Syria, were among states announcing extra security measures.
Belgian Prime Minister Charles Michel spoke of "a black time for our country".
"What we feared has come to pass. Our country has been struck by attacks which are blind, violent and cowardly."
The blast hit the train as it left Maelbeek station, close to European Union institutions, heading to the city center.
The VRT public broadcaster carried a photograph of a metro carriage at a platform with doors and windows completely blown out, its structure deformed and interior mangled and charred.
A local journalist tweeted a photograph of a person lying covered in blood among smoke outside Maelbeek metro station, on the main Rue de la Loi avenue which connects central Brussels with the EU institutions. Ambulances were ferrying the wounded away and sirens rang out across the area.
"WE ARE AT WAR"
“We are at war and we have been subjected to acts of war in Europe for the last few months," French Prime Minister Manuel Valls said.
Public broadcaster VTM said the Tihange nuclear power plant had been evacuated as part of the security clampdown.
Brussels airport said it had canceled all flights until at least 6 a.m. (0500 GMT) on Wednesday and the complex had been evacuated and trains to the airport had been stopped. Passengers were taken to coaches from the terminal that would remove them to a secure area.
All three main long-distance rail stations in Brussels were closed and train services on the cross-channel tunnel from London to Brussels were suspended.
Security services have been on a high state of alert across western Europe for fear of militant attacks backed by Islamic State, which claimed responsibility for the Paris attack.
While most European airports are known for stringent screening procedures of passengers and their baggage, that typically takes place only once passengers have checked in and are heading to the departure gates.
Although there may be discreet surveillance, there is nothing to prevent member of the public walking in to the departure hall at Zaventem airport with heavy baggage.
Following an attempted ramraid attack at Glasgow Airport in 2007, several airports stepped up security at entrances by altering the pick-up and drop-off zones to prevent private cars getting too close to terminal buildings.
European stocks fell after the explosions, particularly travel sector stocks including airlines and hotels, pulling the broader indices down from multi-week highs. Safe-haven assets, gold and government bonds rose in price.
The attacks appeared to be linked to the arrest of French citizen Salah Abdeslam - the prime surviving suspect for November's Paris attacks on a stadium, cafes and a concert hall - who was captured by Belgian police after a shootout on Friday.
Belgium's Interior Minister, Jan Jambon, said on Monday the country was on high alert for a revenge attack.
It was not clear what failings if any allowed the plan for Tuesday's operation to go ahead and whether the double attack was planned in advance or put together at short notice.
"We know that stopping one cell can ... push others into action. We are aware of it in this case,"