By Christian Hartmann and Philip Blenkinsop
SION, Switzerland/BRUSSELS (Reuters) - Belgian military aircraft began returning home the bodies of 22 children and six adults killed in a bus crash in Switzerland on Friday as the country prepared to observe a minute's silence to remember the victims.
White coffins were loaded into Hercules transport aircraft near the Swiss town of Sion as police continued to investigate how the coach, carrying 52 passengers, crashed into the wall of a tunnel on Tuesday night.
Belgium is holding a day of mourning to remember the victims, most of them 12 years old, who were returning from a ski trip to the Belgian towns of Heverlee and Lommel.
A minute of silence will be observed around the country at 11 a.m. (1000 GMT) and churches and cathedrals planned to ring bells for several minutes after the silence. Radio stations changed their playlists to reflect the somber mood.
Flags were flown at half-mast on public buildings across Belgium, the Netherlands and the Swiss canton of Valais where the accident happened.
Six Dutch children were killed in the crash and a further four were injured. Official British sources said one of the dead was an 11-year-old with joint Belgian-British nationality.
Swiss authorities were carrying out an autopsy on the bus drivers' bodies to see if they might yield clues to the cause of the accident.
Some Belgian and Swiss media reported that the driver had been occupied loading a DVD just before the crash, saying this is what some survivors had told their parents, but a Swiss prosecutor cast doubt on the theory.
Christian Varone, chief of police of the Swiss canton of Valais, where the accident happened, said there were many possible explanations for the crash and that police would take into account statements from children.
Six children who survived with minor injuries returned home on Thursday, Belgian authorities said. A Swiss hospital spokeswoman said a further two were also on their way, leaving 16 still in hospital, including three in critical condition.
Late on Thursday some 2,500 people attended a wake in and around the little church of St Joseph's in Lommel, the small town near the Dutch border from where 17 of the dead - 15 children and two school staff - came.
Friday's national day of mourning is Belgium's first since 2004, called to remember 24 people killed in a gas explosion near the town of Ghislenghien.
(Writing by Emma Thomasson; Additional reporting by Michael Holden; Editing by Ben Harding)