As the refugee crisis blew out of proportion, the UN High Commissioner for Refugees (UNHCR) started putting pressure on European Union states to adopt a cohesive policy towards the migrant flows - the greatest seen globally since World War II.
The European Union's response to the refugee crisis will be a "defining moment" for the bloc, the head of the UN refugee agency Antonio Guterres said on Friday, warning that a divided EU would benefit only smugglers and traffickers.
EU leaders, however, are split over sharing the refugee burden and are scrambling to agree a response to the UN demand that could end up making Europe a nation of refugees.
With supporting countries such as Greece, Hungary and Italy, already under pressure, he said, the EU needs to help more migrants enter legally and provide about 200,000 relocation places on an immediate basis.
In Hungary, hundreds of refugees are locked in a stalemate with authorities.
Migrants hoping to reach the Austrian border have refused to disembark from a train surrounded by police in the Hungarian town of Bicske, 40km from Budapest.
Hungarian authorities want to move the migrants to a nearby refugee camp - but the migrants fear registering there will hamper their plans to seek asylum in Germany and other countries.
In the Hungarian capital, Budapest, hundreds of stranded refugees have vowed to "walk to Vienna" because they have not been allowed to board trains.
Hungary has also shut its main border crossing with Serbia after some 300 migrants escaped from a camp in the town of Roszke, prompting a police search operation.
Hungarian MPs have approved tougher border controls and penalties for migrants trying to pass through to their preferred destination, Germany.
Members of the European Commission are in the Greek island of Kos to examine the difficulties caused by the large numbers of refugees and migrants landing there.
The leaders of Poland, the Czech Republic, Slovakia and Hungary will hold an extraordinary summit in Prague.
The UK government - under pressure over its response to the crisis - has agreed to provide settlement for "thousands more" Syrian refugees.
Some 50 migrants are feared to have drowned after their boat sank off the coast of Libya, according to the International Organization for Migration
"This is a defining moment for the European Union, and it now has no other choice but to mobilize full force around this crisis. The only way to solve this problem is for the Union and all member states to implement a common strategy, based on responsibility, solidarity and trust."
The EU has borne relatively little of the rising refugee burden of the Syrian war, which has created 4 million refugees in neighbouring countries and displaced a further 7.6 million within the country.
No EU country could refuse to do its part, Guterres said, and all must make "fundamental changes" to allow more resettlement and humanitarian admissions and to expand visa, sponsorship and scholarship programmes and other ways to enter legally.
"Solidarity cannot be the responsibility of only a few EU member states," said Guterres, a former prime minister of Portugal.
More than 300,000 people have risked their lives this year trying to cross the Mediterranean, and more than 2,600 people have died doing so.
Guterres said the image of a drowned 3-year-old Syrian boy washed up on a Turkish beach that has swept across social media this week had "stirred the hearts of the world public", but the EU had so far failed to find a collective common response.
"Europe is facing a moment of truth. This is the time to reaffirm the values upon which it was built."
(See: UN-backed agency warns of catastrophe as refugee numbers swell)