Nearly 14,600 sheep have died in the Black Sea off the coast of Romania after a cargo ship capsized shortly after leaving the country's Midia port.

Rescue workers managed to save only 33 sheep since the Queen Hind overturned for yet unknown reasons on Sunday.

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The crew of 20 Syrians and one Lebanese were rescued, according to Ana-Maria Stoica, a spokeswoman for the rescue services.

Rescuers supported by the military, police and divers tried on Sunday to right the Palau-flagged ship and pull it to the port, she said.

According to Romania's Digi24 online newspaper, the losses were estimated at three million Romanian lei (nearly $700,000).

Romania's main livestock breeder and exporter association, ACEBOP, called for an urgent investigation.

"Our association is shocked by the disaster," Mary Pana, ACEBOP president, said in a statement. "If we cannot protect livestock during long-distance transports, we should outright ban them."

Gabriel Paun of NGO Animals International alleged the ship had been overloaded. He added that the Queen Hind was known to have engine problems as early as last December.

"An investigation must be opened without delay," he told AFP news agency.

Romania, which joined the European Union in 2007, is one of its poorest members.

It is the bloc's third-largest sheep breeder, after the United Kingdom and Spain, and a top exporter, primarily to Middle Eastern markets.

Activists have labelled the livestock transport vessels - about 100 of which leave Midia every year - "death ships", saying sheep risk being cooked alive on board during the hot summer months.

In July, Vytenis Andriukaitis, then European commissioner in charge of health and food safety, demanded that Bucharest stop the transport of 70,000 sheep to the Gulf, citing animal welfare.

He has asked the European Commission to investigate Romania's practices.