Romanian rescue teams on Saturday were scouring the Black Sea for three Syrian sailors who went missing when their cargo ship sank off the coast, the naval authority said.

The Mohammed Z sank with 11 crew on board, 26 nautical miles off the Romanian town of Sfantu Gheorghe in the Danube delta in the Black Sea on Saturday morning, officials said in a statement.

The ship sailing under the Tanzanian flag was carrying nine Syrian and two Egyptian nationals, it said. 

After receiving an alert at "around 4:00am", naval authorities and border police were dispatched, with two nearby commercial vessels also joining the search and rescue operation.

Eight sailors were rescued by one of the nearby commercial vessels, while the search for the other three, "all of Syrian nationality", was continuing, the statement said. 

The cause of the accident was unclear.

According to the specialist website Marine Traffic, the ship departed from the Turkish port of Mersin and was heading to the Romanian port of Sulina.

Since the start of Russia's war in Ukraine, drifting sea mines have posed a constant threat for ships in the Black Sea, with countries bordering it doubling down on demining efforts.

Ensuring safe passage through the Black Sea has gained particular importance since Romania's Danube ports became hubs for the transit of grain following the Russian blockade of Ukraine's ports.