Pressured by human rights groups and activists to help more than 15,000 refugees and migrants stuck in island detention centers and camps, Greece’s government said more than 600 asylum seekers have been moved from Samos, Lesbos, Chios and Kos to the mainland to ease congestion.

That came after more than 20 groups aiding the refugees and migrants said the centers and camps, including one on Lesbos the BBC called “the worst in the world” were unfit for humans.

Since the beginning of the year, more than 16,500 asylum seekers considered vulnerable have been included in the operation, media reports said.

Those deemed to be vulnerable, that is, single-parent families, the disabled, unaccompanied minors and people suffering from mental health problems, are exempt from the rules of the EU-Turkey Statement and cannot be returned to Turkey and that they are also free to leave the islands of their own accord without limitations.

The 600 refugees will spend their winter in four hotels: 275 people at one in Marathonas, 112 in the area of Stathmos Larissis, 92 in Aghioi Theodoroi, and another 380 in the town of Porto Heli, in Argolida.

There are some 64,000 of them being detained during a suspended European Union swap deal with Turkey.