Police said 10 others were injured in the crash. All 16 people had been crammed into what police described as a "jeep-like vehicle," heading towards the Greek town of Alexandroupolis.
The incident occurred in the Loutra region of Evros, an area on Greece's border with Turkey. Initial information suggested the victims were all adult males, police said.
Hundreds of thousands of people have used Greece as a gateway to other countries in recent years, fleeing violence or poverty in the Middle East and beyond. The numbers have fallen since 2016 after the European Union reached an agreement with Turkey to send people back.