Fresh clashes have broken out on the Greek island of Lesbos between police and migrants desperate to move to the European mainland.
TV footage showed police using batons to control a crowd that was waiting to get onto a ship that had arrived to take several hundred to the port of Piraeus, near Athens.
It comes after a minister in the Greek government told a local radio station that the island was "one step from an explosion".
Up to 20,000 migrants are waiting in the capital Mytilene - with more than two-thirds described as living in "miserable" conditions.
Many of the migrants have been frustrated at the slow pace of the registration process that they need to undergo before they can buy a ticket for a boat to mainland Greece.
Sky's Jonathan Samuels, who is in Lesbos, said: "It's a pretty desperate situation. They are completely inundated with refugees.
"We've seen babies being breastfed on the sidewalk this morning. Toddlers in quite a lot of distress, just unable to cope with the situation.
"There are no washing facilities, there is water, no food and no power.
"We've seen clashes and migrants and refugees storming the office where registration takes place."
The migrants and refugees on Lesbos are part of the migration crisis that has been affecting Europe over the summer.
The UN refugee agency UNHCR said the number of migrants crossing the Mediterranean was expected to pass 400,000 this year, up from 219,000 in 2014.
UK Prime Minister David Cameron said that Britain would take in 20,000 refugees from Syria , but said they would come directly from camps around the war-torn country.
The White House says it is reconsidering the steps the US can take to help Europe deal with the crisis.
Germany, which has seen an influx of migrants after it said anyone seeking asylum was welcome, said other EU countries need to take more.
German Chancellor Angela Merkel reiterated Germany's belief that Europe needs a joint system for dealing with asylum seekers, based on binding quotas.
She said: "This joint European asylum system cannot just exist on paper but must also exist in practice - I say that because it lays out minimum standards for accommodating refugees and the task of registering refugees,"
Her Vice Chancellor Sigmar Gabriel said on Monday that if countries in eastern Europe and elsewhere continued to refuse to take their fair share of refugees, the bloc's open border system, known as Schengen, would be at risk.
On Tuesday, he told TV station ZDF that Germany expects in the order of a half-milllion more migrants a year for the next few years in addition to the 800,000 it is already expecting.
The Dutch, Spanish, Swedish and Austrian governments also backed a quota system, with Austria's Chancellor saying that any nations that do not accept their share should suffer financial penalties.
Poland's president, however, made his opposition to quotas clear.
Failure by authorities to deal with the huge numbers on the move is leading to unrest.
Migrants have been involved in scuffles with police and stampedes as they try to move beyond Hungary's border with Serbia at Roszke.