Belgium observed a moment of silence on Wednesday to mark the first anniversary of the Islamic State bombings in Brussels, beginning a day of emotional ceremonies designed to show that the heart of Europe stands defiant.

A sombre King Philippe and Queen Mathilde, along with Belgian Prime Minister Charles Michel and other ministers, lined up quietly at 7:58 am (0658 GMT) outside the renovated Zaventem Airport to mark the exact time when two suicide bombers killed 16 people and wounded many more at the site.

During the airport ceremony, a woman clutched white roses as Eddy Van Calster, the brother of airport check-in agent Fabienne Van Steenkiste, who was killed in the attack, played a rock ballad in tribute.

As hundreds of people including victims' family members and rescue workers looked on, an airport official read out all of the names of all of the victims. "March 22 2016, will forever be in our hearts...we stand here united," the official said.

The royals will lead a second moment of silence at 9:11 am at Maalbeek subway station to mark the moment a third suicide bomber killed another 16 people on a crowded train.

More than 320 people were wounded in both attacks.

In act of defiance and solidarity, the event at Maalbeek is due to be followed by applause and a "minute of noise" as trains, trams and buses come to a halt in memory of the victims of the country's worst ever terror attacks.

The king and queen will inaugurate a new steel memorial at the heart of the European Union institutions based in Brussels.

A year on, Belgium remains on high alert with troops patrolling the streets and warnings of fresh risks from Islamic State jihadists returning home from Iraq and Syria.

Investigators say the blasts were carried out by a network that was also behind the November 2015 Paris attacks, in which 130 people were killed, and acted on orders from the IS high command.

Ibrahim El Bakraoui and Najim Laachraoui struck at the airport while Bakraoui's brother exploded his bomb at the metro station.

While tightly guarded, Wednesday's ceremonies focus on bringing Belgian society together, from royalty to schoolchildren, and from people of all faiths.

"Today we remember the victims of the attacks. We all remain united," Michel tweeted.

During the "minute of noise", commuters will be invited to take part "to show that they do not forget but they will stay standing against hate and terror", said the Brussels public transport company Stib.

'Resistance and dignity'

Later, children from schools in Molenbeek, the largely Muslim area where many of the attackers hailed from, will meet victims of the attacks in a show of solidarity.

Three marches by Brussels residents will then meet at the Place de La Bourse which was transformed into an impromptu, flower-strewn memorial after the attacks last year.

Finally Brussels' most famous landmark -- the Manneken Pis statue of a little boy -- will be dressed up in a fireman's outfit to hail the efforts of rescue services.

"Over the years Manneken Pis has been stolen, dismounted and broken into pieces. But he is still there and is for us a witness of resistance and dignity," said Tanguy du Bus de Warnaffe, the head of the Brussels fire service.

The shock of the attacks was compounded by accusations afterwards that Belgium had become a "failed state" which was unable to track down the cell behind the Brussels bombings and also the Paris attacks in which 130 people died.

Victims and their families have also complained about the difficulties of getting compensation from Belgian authorities.

Questions abounded about whether deep divisions between Belgium's French and Flemish speaking communities had allowed growing radicalism to slip under the radar.

Fugitive Paris attacker Salah Abdeslam was shot and arrested in a police raid in Molenbeek on March 18, 2016, raising speculation about how he had managed to return to Belgium and remain undetected for nearly four months.

His arrest apparently panicked the rest of the cell into changing their plans and, instead of carrying out a new attack on France, they targeted the airport and metro in Brussels just four days later, investigators say.

A third airport attacker whose device failed to go off, Mohamed Abrini, was arrested in Brussels nearly a month after the attacks.