Thousands of stranded migrants are being evacuated from the makeshift Idomeni camp on Greece's northern border with Macedonia.
Most are being taken to specially designed processing facilities some 80km (50 miles) south, near Greece's second city, Thessaloniki.
Hundreds of riot police moved into the camp at dawn, but the authorities have stressed force will not be used.
The Greek-Macedonia border was closed in March.
Since then at least 8,400 people - many of them women and children - have remained stranded in the border area, having been prevented from continuing their journey to northern Europe.