"The man, aged 19-years-old, was hidden near the gear box, attached with a belt," Elzbieta Pikor, spokesperson for the Polish border guard, told AFP.
Polish transport mechanics had discovered him as they were checking the bus.
"Italia?" the young man asked as he emerged from his hiding place after the 2 800-kilometre (1 700-mile) journey.
In fact, he had arrived in Nowa Deba, southern Poland, having picked the wrong bus, another from the same line having left Athens for Italy.
"He was exhausted, frozen and starving, but in good health," said Pikor.
The would-be immigrant had travelled through Macedonia, Serbia, Hungary and Slovakia along the way, the gear cable scratching his face every time the bus changed gears.
He was carrying no papers and gave his name only as Yahiya, saying he was from the Afghan capital Kabul.
He will be kept in a Polish detention centre pending a decision on his request for refugee status. – AFP