Belgian military planes are bringing home the bodies of 28 people, mostly children, killed in a bus crash earlier this week in a Swiss tunnel.

Belgian officials declared Friday a national day of mourning, as the memorials outside two Catholic schools attended by nearly two-dozen victims continue to grow.

Authorities say all the victims have been positively identified.

Seven Dutch citizens and 21 Belgians were killed when the bus struck the wall of a tunnel Tuesday in the Valais region while returning from a ski trip. The victims include two drivers, adult staff and 22 children from Belgium.

Eight crash survivors were flown back to Belgium late Thursday.

The cause of the bus crash near the town of Sierre has not been determined. Swiss officials say the vehicle was traveling at a normal speed.