The first two boats deporting would-be refugees back to Turkey have set sail from Greece as part of the EU migrant transfer deal to limit the numbers arriving in Europe.
A spokesperson for the EU border protection agency said the process involving the first 135 migrants, mostly from Pakistan and Bangladesh, had gone smoothly.
The failed asylum-seekers were expected to be returned by Turkey to their country of origin - sparking renewed concerns as to what will happen to refugees arriving from war zones.
Police and border agents appeared to get the jump on reporters on Monday morning, moving the first groups of refugees under heavy security considerably earlier than expected.
Leaving the Greek island of Lesbos, they were expected to arrive shortly at nearby ports on the Turkish coast a short while later.
About 4,000 migrants and refugees have been detained on Greek islands since the migrant transfer agreement came into effect on 20 March.
On nearby Chios, there were clashes with local residents just hours earlier following a protest against the planned deportations there.
No Syrians were present in the first group of migrants coming to Turkey from Greece on Monday, Turkish EU Affairs Minister Volkan Bozkir said.
Bozkir also told broadcaster Haberturk TV that any Syrians who arrive in future will be sent to the southern Turkish city of Osmaniye.
Syrians being sent directly to Europe as part of the exchange deal would be given safe passage to Germany, from where some will be moved on to other countries.
The first vessel, the Nazli Jale, reached the port of Dikili accompanied by the Turkish coast guard.
Turkey's state-run Anadolu Agency put the number of migrants at 131 and said they were mostly Pakistani nationals. A Turkish government official told the AP authorities were expecting 202 people. The official spoke on condition of anonymity because he was not authorized to speak publicly on the issue.
A total of 50,000 migrants and refugees are stranded in Greece following EU and Balkan border closures, but only those who arrived after March 20 will be detained for deportation.
Additional reporting by agencies
