Serbia's customs authorities said Friday they discovered nine migrants hiding among aluminum rolls in a truck headed to Poland from Greece.

Customs officers on Serbia's border with North Macedonia spotted the migrants on Wednesday during a scan that showed human silhouettes in the back of the truck, a statement said.

The migrants were young men from Afghanistan, Pakistan and Syria, the statement added.

Serbia lies at the heart of the so-called Balkan land route that refugees and migrants use to try to reach Western Europe and start new lives there.

Migrants go from Turkey to Greece or Bulgaria, then to North Macedonia and Serbia. From Serbia they move on toward European Union member states Hungary, Croatia or Romania, or they go to Bosnia first and then on to Croatia.

Thousands of people fleeing violence or poverty pass through the Balkan region every year. They often face dangers in the hands of people-smugglers who help them cross borders undetected.