Two Ukrainian sailors died and a third went missing when a cargo ship sank in the Black Sea off Romania on Thursday, Romanian naval authorities said. 

"The Volgo Balt 179 ship with 13 Ukrainian crew members aboard, including a woman, sank," said the GSP company in charge of the rescue operation.  

Ten sailors were rescued after the crew sent a distress signal before dawn, but two had died while the search for another sailor continued, GSP said on its website.

A helicopter was deployed to "evacuate the only female crew member, whose condition worsened". 

The vessel ship was on its way to deliver Russian coal to the Romanian port of Constanta, Agerpres agency quoted the Romanian navigators' union as saying. 

The coastguard also dispatched a boat but a spokesperson told AFP the weather conditions were "very unfavourable".