Greek police arrested a Slovenian truck driver, who was planning to bring 35 migrants, including children, in a hollow compartment of a truck to the Macedonian border.
The truck driver, who was arrested near the port city of Thessaloniki, was charging 1,300 euros (1,471 dollars) for the trip, police said Monday.
The people found in the truck included 12-year-old children.
At least 57,000 migrants are stuck in the south-western European nation, since the so-called Balkan route from Greece to northern Europe was closed in Marched.
While border measures have stifled the massive flow of migrants, people are still making their way through the Balkans, often paying traffickers to provide transport along stretches of the journey.
In Belgrade on Monday, Serbian police said they had arrested one member of a trafficking group driving a van with 53 migrants crammed inside. International and local aid organizations estimate that 200-600 people filter through Serbia daily.
Czech authorities on Monday dispatched a contingent of 40 police officers to help Macedonia patrol its border with Greece.
The unit, the third sent to Macedonia since it sealed its border to irregularly arriving migrants in February, will be armed for self-protection while on patrol with its Macedonian counterparts during a renewable six-month mission.