The United Nations has expressed concern about a lack of preparation for the planned return of migrants from Greece to Turkey.
Several hundred people are due to be moved today under a deal struck between the European Union and Turkey.
There are concerns about whether appropriate safeguards and logistics are in place.
In the Turkish coastal town of Dikili, a small number of white tents have been set up along the port.
The town will soon become a designated registration point for hundreds of migrants expected to be returned from Greece as part of a deal between the European Union and Turkey.
Hundreds of Turkish residents have protested ahead of the planned move.
They say it is not sustainable for the number of migrants in Turkey to increase and they are concerned about security.
The deal is aimed at easing the uncontrolled mass movement of people into Europe.
From today, migrants arriving illegally in Greece are to be sent back to Turkey if they do not apply for asylum or their claims are rejected.
For every Syrian returned, one Syrian will be resettled to Europe directly from Turkey.
A spokesman for the United Nations refugee agency the UNHCR, Boris Cheshirkov, says refugees and migrants in Lesbos are being warned about the process.
But he says there is concern about necessary safeguards being implemented.
"We're trying to provide counselling on the rights and procedures to seek asylum to as many (people) as we can. We've also seen encouraging steps from the authorities trying to identify people with specific needs and at heightened risk, which is an encouraging sign. But at the same time, if reports as we are hearing them coming through (are right), with returns meant to take place already tomorrow, we haven't seen the necessary level of safeguards, and we are urgently calling for these safeguards to be in place before any of the returns are possible."
So far, more than 6,000 migrants have been registered on the Greek islands since the agreement came into force two weeks ago.
Mohammad Arqam, a 20-year-old man from Pakistan, says he is not sure where he will be sent or when.
"If we go, he say you will be deported, you cannot arrive to apply for asylum, you cannot get your lawyer. Policemen pressurise you. When we come to apply, my friends (and me), some of my friends, go and try to (apply for) asylum, he is ... he will be arrested and thrown in Turkey."
Greece's parliament passed an asylum amendment bill on Friday needed to implement the agreement.
The legislation does not explicity designate Turkey as a safe third country.
The president of the Research Centre on Asylum and Migration, Metin Corabatir, says there are gaps in the deal.
"This deal, in its current shape, if it is implemented like this, it will harm the people, these poor people. It will be a second trauma. They are already experiencing second, third, fifth traumas. And this will be the next trauma."
In northern Italy, there are tensions, too, over the strict control of the Northern Brenner border with Austria.
Protesters have scuffled with riot police while calling for an open-border policy and for migrants and refugees to be welcomed.
Austria's defence minister says soldiers will now be deployed at the Brenner Pass.
He claims the European Union's outer borders are not being protected properly.
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