A second wave of migrants is being sent back from Greece to Turkey as part of an EU deal to reduce the numbers reaching Europe.
Buses brought groups of migrants to ports in the Greek islands, where they were escorted onto a boat by police.
There are thought to be Syrians among the latest arrivals.
The first group of about 200 mainly Pakistanis arrived on Monday but the process stalled, partly due to a surge in asylum applications in Greece.
Under the EU deal with Turkey, migrants who have arrived illegally in Greece after March 20 are expected to be sent back to Turkey if they do not apply for asylum or if their claim is rejected.
And for each Syrian migrant returned to Turkey, the EU is due to take in another Syrian who has made a legitimate request.
Greek customs officials told the BBC that 140 people would be travelling on two boats on Friday, the first carrying 45 from Lesbos and the second bringing 95 more from other islands.
Of those being returned to Turkey on Friday, the non-Syrians will be taken to deportation centres while any Syrians will be taken to refugee camps to take the place of Syrian refugees who will be directly resettled in the EU.
But Turkey’s President Recep Tayyip Erdogan said on Thursday that his country will only implement this deal if the EU sticks to its side of the bargain:
*A further 3bn euros ($3.4bn)
*Galvanising Turkey’s EU accession process
*Granting Turks visa-free travel to the EU’s Schengen area by the end of June
“There are precise conditions. If the European Union does not take the necessary steps, then Turkey will not implement the agreement,” Erdogan said in a speech at his presidential palace in Ankara.
But German Chancellor Angela Merkel, whose country has taken in the bulk of the asylum seekers so far, was more upbeat.
“I am very happy today. However, I know that we have not yet completed all the tasks before us,” she told a news conference during a meeting with French counterpart Francois Hollande in eastern France.
The arrangement has alarmed rights groups, who say Turkey is not a safe country for migrants.
Amnesty International has accused Turkey of illegally returning Syrians to their homeland, something Turkey denies.
On Thursday Amnesty also raised the alarm on the lack of information and help available for migrants on the Greek islands.
People detained on Lesbos and Chios have virtually no access to legal aid, limited access to services and support, and hardly any information about their current status or possible fate,” said Amnesty Deputy Director for Europe Gauri van Gulik.
“The fear and desperation are palpable,” Reuters quoted her as saying.
“They show that in addition to Turkey not being safe for refugees at the moment, there are also serious flaws on the Greek side of the EU-Turkey deal.”
