Nine suspected drivers for migrant smuggling rings have been arrested in northern Greece in a single day with up to 12 passengers squashed into their cars, police said Thursday.

Six of the arrests were made Wednesday in the northeastern Evros region on Greece’s land border with Turkey, which is a major entry point for migrants. The suspects were carrying a total 48 migrants, in cars designed to take no more than five people each.

Another three suspected smugglers were arrested Wednesday near Thessaloniki, where most undocumented migrants head as their first stop after the Greek-Turkish border.

Thousands of people from the Middle East, the Indian subcontinent and Africa enter Greece every year, hoping to move on from there to seek a better life in Europe’s prosperous heartland.

More than 5,000 people have crossed the Evros border so far this year, despite the fence that Greek authorities have built along much of the frontier line.