ATHENS: Five children, one woman and four men drowned when their boat sank off the small Greek island of Farmakonisi, Greek coastguard officials said early on Wednesday.

Another 13 people, 11 men and two women, were rescued and two were still missing according to witnesses, the officials said adding that a helicopter, a patrol boat and private vessels assisted the search-and-rescue operation.

"The vessel, a 6-metre (20-foot) speed boat, sank under unknown circumstances," one of the officials told Reuters. "They were in the water when they were spotted by a rescue boat."

The incident took place east of Farmakonisi, close to Turkey's coast. Tens of thousands of mainly Syrian refugees have braved rough seas this year to make the short but precarious journey from Turkey to Greece's islands.

More than 1 million refugees and migrants came to the European Union in 2015, while almost 3,700 died or went missing during the journey, which has reaped huge profit for smugglers, the International Organisation for Migration said on Tuesday.

The EU is counting on Ankara to stem the flow of refugees from Turkey into Greece and onward to Germany and other EU countries. A report said there was little evidence of progress since Turkey signed an "action plan" with the EU.

Its neighbour, Greece, which is a gateway to the EU, is also trying to rebuff criticism that it has done too little to manage the people arriving on its shores.

Athens has promised to speed up the construction of EU-assisted reception and registration centres on five islands, but so far only the so-called hotspot on Lesbos is operational.