Some 300 people set up camp in Victoria Square, central Athens, on Wednesday.
Government officials were on Wednesday night trying to find more places to host refugees and migrants as the number of people arriving continued to rise while limits on those leaving remained in place.
Tens of thousands of migrants are thought to be in Greece at the moment, waiting to find a way out after border controls were stepped up north of the country. An official at the Migration Policy Ministry said that the government had made contingency plans for looking after 50,000 people. But these plans may prove inadequate as the Former Yugoslav Republic of Macedonia (FYROM) is only allowing a few hundred migrants to cross from Greece each day.
In contrast, an average of around 3,000 people have been arriving on Greek islands each day this week. on Wednesday, more than 1,700 migrants arrived at Piraeus on passenger ferries from the islands. Greek authorities are trying to find ways, including stopping coaches on the national highway, to prevent all the arrivals traveling to Idomeni, next to the border with FYROM, where some 3,000 people have already gathered. The migrants who have been stopped on their journey north are being housed in motels and sports centers.
The transit centers at Schisto, Elaionas and Elliniko in Athens, as well as Diavata in Thessaloniki have filled up over the last few days. The camps at Schisto and Diavata are hosting around 2,000 people each. There are concerns that the lack of spaces will mean that migrants will start camping out in city squares. Some 300 people set up camp in Victoria Square, central Athens, on Wednesday.