At least 25 people attempting to reach Greece drowned after their boat sank off the Turkish coast, the state-run Anatolian Agency reported.

The Turkish Coast Guard, using speedboats and a helicopter, rescued 15 people and recovered 18 bodies in the Aegean Sea near the town of Didim, it said. Ten of the 25 victims were children.

Elsewhere, some 13,000 refugees are crammed in unhygienic conditions on Greece's border with Macedonia, officials have said with all eyes on a key EU-Turkey summit tomorrow that is seen as the only viable solution to the crisis.

"There are 13,000 people here and nearly 20,000 in this prefecture, over 60 percent of the country's entire refugee and migrant flow," Apostolos Tzitzikostas, regional governor of Greece's Macedonia prefecture, told Skai television yesterday as he visited the border to distribute food.

"We can no longer shoulder this strain by ourselves," said Mr Tzitzikostas, who wants the government to declare an emergency in the area.

Greece has been plunged at the heart of Europe's greatest migration crisis in six decades after a series of border restrictions along the migrant trail, from Austria to Macedonia has caused a bottleneck on its soil.

Over 30,000 refugees and migrants have been trapped in the country, around a third of them at Idomeni where aid groups have long reported food and tent shortages.

The Doctors Without Borders charity yesterday began erecting additional tents to shelter over 1,000 people who have been sleeping in muddy fields and ditches, an AFP reporter said.

In past days, the mainly Syrian and Iraqi refugees have regularly held protests in front of the barbed-wire fence guarded by Macedonian riot police, demanding to be allowed through.

On Monday, hundreds of them tried to break through a breach in the fence, and were pushed back with volleys of tear gas.

According to Greek officials, Macedonia has allowed some 2,000 people through its borders in the last two weeks. The same number of people fleeing war and poverty arrive in Greece from neighbouring Turkey in two days.

Athens is building additional facilities to house the refugees and migrants, but many prefer to go to the border in the hope of eventually getting through, and are stuck there for days and weeks.

Greece has asked the EU for €480m in emergency funds to help shelter 100,000 refugees. A senior UN migration official has warned that the numbers stuck in Greece will probably reach 70,000 in the coming weeks.