The 16-year-old Bangladeshi national had apparently travelled from Serbia to Switzerland hidden among goods in the trailer, according to information from St Gallen police.
The teenager was discovered as the lorry was about to be unloaded in an industrial park in the northeastern Swiss canton of St Gallen.
He had apparently secretly entered the trailer through the tarpaulin cover in Serbia. Police did not give details about why the adolescent had undertaken the perilous journey. The 16-year-old was handed over to asylum authorities.
The truck had apparently already been given a customs seal in Turkey, but there is no suggestion the driver or the company were complicit in people smuggling.