Belgium was to hold a national day of mourning Friday for the 28 people who died this week when a bus carrying children on a school skiing trip crashed in a Swiss highway tunnel, DPA reported.
A minute of silence is to be observed at 11 am (1000 GMT), the Belgian government said.
In the Netherlands, where six of the victims were from, Prime Minister Mark Rutter ordered flags on government buildings to fly at half-staff.
The technical examination of the remains of the bus is to also begin Friday.
The Belgian government dispatched three planes to Switzerland to return home the more than 100 relatives of the accident victims there and bring some of the 24 injured children and the bodies of the 28 victims to Brussels.
The Belga news agency reported that the first injured children and relatives returned early Friday, landing at a military airport in the Belgian capital.
Tuesday's crash killed 22 children and six adults when their bus crashed head-on into the wall of an emergency bay of a tunnel in the southern canton of Valais.
The children were about 12 years old and came from two schools in the Flemish part of Belgium, one in Lommel near the Dutch border and the other in Heverlee near Leuven.
Thousands of people in both cities attended church services Thursday night for the dead and injured.
Three of the children suffered life-threatening injuries and were among four who could not yet be transported.
The cause of the accident remained unknown. Swiss police described a report by the Belgian newspaper Het Laatste Nieuws that said the accident happened as the driver changed a DVD as "pure speculation."