The United Nations refugee agency called on Greece on Friday to take control of the "total chaos" on Mediterranean islands where thousands of migrants have landed.
European Union member states must also do more to share the burden of Greece, where 50,000 people arrived in July alone, said Vincent Cochetel, UNHCR director for Europe, after visiting the Greek islands of Lesvos, Kos and Chios.
"In terms of water, in terms of sanitation, in terms of food assistance, it's totally inadequate. On most of the islands, there is no reception capacity, people are not sleeping under any form of roof," he told a news briefing.
"So it's total chaos on the islands. After a couple of days they are transferred to Athens; there is nothing waiting for them in Athens."
Greek authorities must "lead and coordinate the response," said Cochetel, a 30-year veteran of the UN High Commissioner for Refugees who said he had "never seen a situation like that."
"We are concerned with the situation where no one is really assuming leadership in the response, which makes it very difficult for humanitarian operators to participate in the efforts," he said.
Cochetel voiced concern that the situation not degenerate in Greece or be "exploited" for political ends.
"The top priority is not to let other Calais develop in other places of Europe," he added. Many migrants head for the French port, and at least 10 have died trying to enter Britain through the Channel Tunnel.