In the latest humanitarian disaster to strike refugees trying to get to Europe, at least 25 people are reported to have drowned off the Turkish coast while trying to reach Greece.
The coastguard launched a search-and-rescue mission for other people believed to be missing from the accident near the Turkish town of Didim.
At least 15 people were rescued and brought to land in the care of emergency aid workers.
Sunday's incident came as European Union leaders prepared to meet to discuss the mounting refugee crisis on the Greek-Macedonia border, where about 13,000 people are living in precarious conditions as they wait for authorities to let them into Macedonia so they can move towards Western Europe.
The UN High Commissioner for Refugees (UNHCR) said a humanitarian crisis was quickly unfolding at the border, with refugees living in makeshift camps and in the open, as authorities allow only 250 a day to pass through.
"It's a wake-up call for the EU leaders, because this is a humanitarian crisis," the UNHCR's Babar Baloch said.
He said the situation at the border could not persist for long.
The situation is rapidly deteriorating, with more people arriving daily, observers said.
Al Jazeera's Hoda Abdel-Hamid, reporting from the Idomeni refugee centre on the Greek side of the border, said the bottleneck occurred suddenly and that Greek authorities were trying to open a reception centre to address the growing needs.
Baloch said about 55 percent of the people at the Idomeni camp - which was designed for 2,000 people - are women and children.
People have taken to camping in the open in nearby fields. Many of the children are reportedly suffering from respiratory diseases.
The EU has planned a crisis summit in Brussels with Turkey on Monday to discuss the refugee issue.
Many of the asylum seekers fleeing conflict in the Middle East first head to Turkey, from where they move on to Greece before hoping to make the trip further into Europe.
EU leaders will hope to persuade Ahmet Davutoglu, Turkey's prime minister, to slow the flow of people and take back thousands who do not qualify for asylum.
They will also be looking at how to seal the Balkans route and boost aid to Greece in an attempt to restore unity among the 28 member nations.
READ MORE: Greece refugee crisis - Border area at breaking point
Apostolos Tzitzikostas, governor of Greece's Central Macedonia province, called on the government on Saturday to declare a state of emergency for the area surrounding the Idomeni border crossing.
"It's a huge humanitarian crisis. I have asked the government to declare the area in a state of emergency," Tzitzikostas said during a visit to Idomeni to distribute aid to the Red Cross and other non-governmental organisations.
"This cannot continue for much longer."
Reporting from Idomeni on Saturday, Al Jazeera's Abdel-Hamid said: "Once [the emergency] is in place - and that will not be before Monday - it would mean there is a release of emergency funds, first 200,000 euros, to help out in this camp, provide more tents, food, blankets and facilities. There is no running water here."
Source: Al Jazeera And Agencies