Nineteen people died when a boat carrying about 150 migrants sank off the coast of northern Cyprus, and rescuers were searching for 25 other people, Turkey's coast guard said on Wednesday.

It said 103 migrants were rescued by boats and helicopters of the Turkish and northern Cypriot coast guards, helped by commercial boats in the area, from the sunken boat some 30 km off the north Cyprus coast.

One rescued person was in critical condition and has been brought to northern Cyprus by helicopter, the coast guard said.

Burhanettin Kocamaz, mayor of the southern Turkish province of Mersin, told broadcaster Haberturk that the rescued migrants and the bodies of those killed in the sunken boat were being brought to Mersin.

Kocamaz said there was no information about the origins of the migrants yet, adding authorities did not yet know where the migrant boat had come from.

Television footage of the passengers' arrival showed several ambulances arriving at Mersin's Tasucu harbor, from where they were taken to the Silifke district for treatment.

The coast guard said a Panama-flagged commercial ship spotted the migrant boat some 25 nautical miles from Turkey's southern province of Antalya and alerted the coast guard on Wednesday morning.

In 2015, Turkey became one of the main launch points for more than a million migrants taking the dangerous sea route to the European Union, many fleeing conflict and poverty in the Middle East and Africa.

A 2016 deal between Turkey and the European Union sharply reduced the flow of refugees into the bloc, after thousands died crossing from Turkey to Greek islands a few miles offshore.

From January to May this year at least 26 migrants died trying to cross to Europe from Turkey, according to coast guard statistics.

Mediterranean arrivals to the bloc, including refugees making the longer and more perilous crossing from north Africa to Italy, stood at 172,301 in 2017, down from 362,753 in 2016 and 1,015,078 in 2015, according to data from the United Nations