The Belgian and Dutch royal families will  gather on Wednesday, 21 March at a memorial ceremony for 17 victims from a Belgian school who died in a Swiss bus crash, the town's mayor said Friday.

"We can announce that the Belgian royal family and also the Dutch royal family will attend the memorial ceremony" on Wednesday, Peter Vanvelthoven, the mayor of this north-eastern border town, told a news conference.

Twenty-eight people, including 22 children from Belgian schools, six of them of Dutch nationality, died in Tuesday night's accident last week.

Fifteen pupils and two staff from the 't Stekske school in Lommel, home to 33,000 people, perished in the tragedy, while six children survived.

The remaining dead were two staff and seven children from the Sint Lambertus school in Leuven, east of Brussels, and the two bus drivers bringing them back from a skiing holiday in Switzerland.

Belgium observed a minute's silence on Friday morning to honour the dead as their bodies were flown back from Switzerland.