As dawn broke, buses filled with migrants left under heavy security from a detention centre on the island of Lesbos headed to the port for the short boat ride to the Turkish port of Dikili.
More were ferried across from the island of Chios, where riot police clashed hours earlier with demonstrators protesting the expulsions.
In all, 202 people from 11 nations, 191 men and 11 women were sent back. They included 130 Pakistanis, 42 Afghans, 10 Iranians, five Congolese, four Sri Lankans, three Bangladeshis, three from India, and one each from Iraq, Somalia and Ivory Coast, as well as two Syrians who Greek authorities said had asked to be sent back.
"The returns underway this morning in the Aegean are the symbolic start of the potential disastrous undoing of Europe's commitment to protecting refugees," said Amnesty International's deputy director for Europe, Gauri van Gulik.
"Urgent key questions are: What process is everyone going through and what will become of them after their return?" Judith Sunderland, acting deputy Europe director at Human Rights Watch, said trying to close the Aegean migration route by shipping people "back to uncertain fates in Turkey" will only make them seek potentially more dangerous and expensive ways to reach the EU.