Europe must help tackle a crisis situation in Greece where roughly 5,000 child migrants live in danger of exploitation and violence, the UN refugee chief said on Thursday.
"There is a children emergency in this country... that needs to be tackled," UNHCR chief Filippo Grandi told reporters after a two-day visit.
Hundreds of migrants arrive on the Greek islands from Turkey every day, adding to roughly 39,000 already housed in island camps and 22,000 more on the mainland.
Last week, the Greek government said it had failed to persuade other EU countries to help host around 3,000 of the children.
"Frankly... if Europe does not feel that it has to share responsibility on children that have no homes, no families and no future, I'm worried about Europe," Grandi said.
Rights groups have criticised Greece's new conservative government for its response to the situation.
The government has sped up asylum procedures and last week unveiled plans to build larger closed camps on the islands, leading to fears that thousands will be locked up before deportation.
"I made it clear to the government that UNHCR policy is against detaining asylum seekers. Seeking asylum is not a crime," said Grandi, who met Prime Minister Kyriakos Mitsotakis and ministers involved with the issue.
Grandi said he found living conditions in the camps he visited on the island of Lesbos "extremely disturbing" with "generalised tension often resulting in violence, especially against minors".
"This country needs to turn the page in how this movement is handled," he said.
Officials on Lesbos and Samos islands have already criticised the planned new camps, which are each intended to hold more than 5,000 people.
Protests have also taken place in several towns in northern Greece in recent weeks to block attempted relocations of asylum seekers.
Greek officials have come under fire from political opponents recently for saying asylum seekers were not entitled to international protection if they do not come from war zones.
"We're all in favour of efficiency and even speed," said Grandi, adding: "None of this must be at the expense of the safeguards... Everybody should be judged in his or her own merit."