All EU flags hung at half staff along the EU Commission headquarters to mark the occasion.
At the KBC bank, automatic teller machines read: "We are speechless. All of KBC shares in the sorrow in silence."
Broadcasters rescheduled their programming, with VTM postponing the live finale of its popular singing contest "The Voice of Flanders" for a day.
Special ceremonies were held at the two schools that shared the bus bringing pupils home from their ski holiday. In Heverlee, the school gates, plastered with children's drawings about the tragedy, opened for the primary school kids to stand in silence before releasing white balloons up in the sky.
On Thursday evening, hundreds packed the Holy Cross Church in Sierre, the city in southern Switzerland where the crash took place, for a memorial Mass.
John Heilprin and Frank Jordans in Geneva, Jeffrey Schaeffer in Sion, Switzerland and Mike Corder in The Hague, Netherlands, contributed to this story.
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