"We're seeing on the one hand increasing closures, and on the other, no openings," U.N. High Commissioner for Refugees Filippo Grandi told a news conference in Athens after a visit to Lesbos, the Greek island that has been a key landing point for desperate migrants entering Europe.
Reluctance of some European countries to take refugees and discussions in Germany to limit the number there have had little effect on the tide of humanity arriving from the east. Three times as many migrants have arrived so far this year in Greece -- by far their main gateway to Europe -- as had by this point last year.
But as migrant boats and rafts cross the Mediterranean Sea and land on beaches in growing numbers, gateways into Europe are narrowing markedly.
More than 100,000 people have arrived in Greece so far this year. Last year, it took until June to reach that number. Countries on the so-called Balkan route to central Europe reacted recently by imposing restrictions.
Grandi warned that the closure of routes into Europe could create a bottleneck in Greece.
"If you block it and you don't create well-managed openings ... then the problem becomes very serious."
Blocking the path of migrants would only give rise to new smuggling networks and threatened to expose other states to "chaos and disorganization," he said.
Rather, he stressed, "restrictions need to be lifted and relocation has to happen."
In many European countries, however, the political tide appears to be moving the other way.
On Wednesday, Hungary's right-wing Prime Minister Viktor Orban announced his government planned to call a referendum on the European Union's mandatory quotas on migrants.
"I am convinced that the government is responding to public sentiment," he told reporters.
"We think that introducing resettlement quotas for migrants without the backing of the people equals an abuse of power."
Orban did not say when the referendum would be held. His government has consistently opposed the EU's compulsory quotas to accept migrants.
Macedonia stopped Afghans from entering from Greece this week, and on Tuesday, when migrants shook and climbed over border fences and barbed wire, Greek police corralled them and brought them back into Greece.
That tightened border was a small part of a bottleneck that reaches all the way to Austria, the Office of the U.N. High Commissioner for Refugees said.
A week ago, Austria announced it would let no more than 3,200 new entries into the country per day and take only 80 applications for asylum per day.
"Slovenia followed suit and announced a similar cap to restrict movements across its borders," the UNHCR said.
A day later, heads of police in countries all the way along the Balkan route announced an agreement to start screening refugees at the Macedonian border with Greece.
"That will create further chaos and confusion. It will increase the burden on Greece, which is already shouldering a very big responsibility in managing these people," said Grandi.
The massive wave of people is already starting to back up at the Greek border.
And Greece is not happy with its neighbors' actions.
"It cannot be tolerated that some member countries do as they want on their own regardless of what everyone else has agreed upon, and this should not be accepted by the European Union
," said government spokeswoman Olga Gerovasili.
In the freezing cold
To get an idea of what a bottleneck could do as the human tide crashes into it: Last week alone, before the measures were announced, 7,286 refugees crossed from Greece into Macedonia, the International Organization for Migration
Last year, 853,650 migrants entered Europe via Greece, and the portion of children arriving bumped up.
Some of the decisions by countries along the Balkan route amount to profiling, the UNHCR said. They select people based on nationality and not the dangers they face from violent conflict at home.
They could also strand people outdoors in freezing weather and make them vulnerable to human traffickers.
In Italy, where many refugee boats also go ashore, the situation is less dire. The country has received more than 7,500 migrants this year. Last year, more than 150,000 migrants arrived there.
On Tuesday, the Italian navy rescued 1,431 people from boats, and it recovered the bodies of eight more.
Altogether, more than 400 migrants have died at sea this year while trying to reach Europe.