Fifteen people drowned and up to 15 more were missing on Friday after a fishing boat carrying migrants sunk off Turkey's Black Sea coast, the coast guard said.

Forty migrants were rescued but search and rescue efforts are under way to find 13-15 people still missing in the incident off the Kefken district, the statement said. The area lies about 130 kilometres (80 miles) east of Istanbul.

One pregnant woman who was rescued was taken to hospital but lost her baby, state-run Anadolu news agency said.

Mehmet Unal, a local official in the nearby town of Kandira, said the boat was believed to be carrying 70 migrants, most of whom were Iraqis.

Unconfirmed media reports said the migrants had boarded the boat in Zonguldak which lies further to the east, and were trying to cross into Romania.

The boat reportedly sank due to bad weather and rough waters. Western Turkey and the Black Sea had been hit by a heavy storm and rains overnight.

Turkey has emerged as a hub for migrants from trouble zones around the world including Syria, Iraq and Afghanistan who are seeking a route west to the European Union.

In 2015, around a million people undertook risky sea journeys to cross the Mediterranean to Europe, mostly to Greece from Turkey over the Aegean Sea.

Thousands died in the perilous crossing. Responding to international pressure, Turkey tightened its sea borders and cracked down on migrant smuggling rings as part of a 2016 deal with the European Union.

The numbers of migrants crossing the Aegean has now dwindled.

But increasing numbers, now rising to hundreds within a month, are now trying to cross the Black Sea from Turkey to EU member Romania.

Some 834 migrants were caught and 10 smugglers detained in seven Black Sea incidents between mid-August and early September, according to statistics published by Anadolu.

Separately, 237 migrants and five organisers were caught in two other incidents in the area whose timing was not specified.