A woman and child have drowned and 33 people were rescued after a boat carrying migrants from Turkey sank off the Greek island of Leros, Greece's coastguard said Sunday.

The survivors, including six children, were transferred to hospital in Leros, with the rescue operation continuing, the coastguard said.

Three rescue boats and a helicopter have been deployed but progress is being hampered by strong winds and choppy seas in the Mediterranean.

A fisherman raised the alarm after discovering the lifeless body of the woman floating at sea, according to local press reports.

Eye witnesses reported seeing an inflatable boat with 40 migrants, including children and people with reduced mobility aboard.

Last December, a two-month-old baby died after a shipwreck off the Greek island of Lesbos.

Some 2,246 people fleeing wars and poverty are known to have lost their lives in the eastern Mediterranean since 2014, according to statistics from the International Organization for Migration (IOM).