(Updates number of crew, rescue operations)

SOFIA, Sept 27 (Reuters) - A North Korean-registered cargo ship with 10 Ukrainian and Russian crew on board sank in rough waters in the Black Sea early on Saturday, Bulgarian authorities said.

Rescuers have so far failed to find any survivors as stormy conditions hampered rescue operations, said Nikolay Apostolov head of Bulgaria's Maritime Administration Agency. Rescue workers have also not found any bodies.

Efforts to save the crew, which consisted of nine Ukrainian and one Russian seamen, will be halted for the night because of the bad weather, he said.

The Tolstoy, which carried 2,500 tonnes of metal scarp and was sailing from Russia to Turkey, sank at about 4 a.m. (0100 GMT) some 12 miles off Cape Emine on Bulgaria's Black Sea coast, officials said. It issued no SOS call, they said.

"We received the exact crew list from the authorities in Rostov (Russia). It shows the ship had 10 not 12 crew, which was the preliminary information," Apostolov said.

He said the vessel was owned by an Ukrainian company and sailed under the North Korean flag. (Reporting by Anna Mudeva; Editing by Matthew Jones)

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