The migrants, most of them Afghans, suffered no injuries during this kind of transport, one of the officials said, adding that the cooling system was not on.
Police stopped the truck for a routine control on a highway near the northern Greek city of Xanthi.
After detecting the migrants inside the truck, police arrested the driver and the migrants were taken for identification to a police station.
Most of the migrants arriving in Greece leave the wars in Syria, Iraq and elsewhere.
Greek authorities are struggling to cope with a sharp increase in the number of migrants to its eastern islands.
EU-funded camps in Greece are overcrowded and in many cases, have been reported violent incidents and casualties.