At least 17 people were reported missing after a refugee ship, with over 30 undocumented migrants onboard, sank in the Aegean Sea, according to Greek media.Sixteen people, including a pregnant woman and a child, were rescued immediately after the ship sank between the Greek islands of Farmakonisi and Agazonisi in an operation carried out by Greek-Turkish rescue teams on Tuesday.Port authorities confirmed that the search operation continues.The nationalities of the passengers were unknown.About 61,000 migrants have arrived in Greece by sea since the beginning of 2015 --double the figure recorded in 2014 -- while 37 died or disappeared, according to the International Organization for Migration.The civil war in Syria that broke out in March 2011 has rendered some four million Syrian refugees in neighbouring countries and about 30,000 of them have crossed to Greece in 2015.