(CNN)Thousands of sheep are feared to have drowned after a cargo ship capsized in the Black Sea off the coast of Romania on Sunday.
The Queen Hind ship, sailing under the flag of Palau, was carrying 14,600 sheep when it partially sank shortly after departing from the Port of Midia, according to state news agency Agerpres. Photos show the ship half submerged in the Black Sea.
A rescue operation was immediately launched, with authorities sending 10 vessels to the scene.
A crew of 22 people were also on board. One fell overboard into the water, but he and the others have been rescued and brought to land, according to Agerpres.
The Coast Guard, the marine rescue agency, and other emergency services were mobilized, working until night fell. As of Sunday afternoon, about 40 sheep had been rescued, Agerpres reported. The operation will continue Monday morning local time.
Photos and video from the scene show some sheep still above water, their heads poking out the ship railings. The few who were rescued were loaded onto dinghies and brought to port.
It's unclear how many sheep are still alive on the ship, but authorities are anticipating the worst.
"They are probably drowned," the inspector general of ISU Dobrogea, the county's emergency response agency, told CNN affiliate Pro TV. "With people, with boats, we'll see what resources we have that we can use."
Authorities have not yet determined what caused the ship to capsize, but an investigation will explore several possibilities, according to Pro TV. One is that the sheep were not properly loaded on board, creating a weight imbalance to one side of the ship, causing it to sink.
Livestock companies and animal rights organizations have expressed outrage at the sinking. ACEBOP, a Romanian association made up of 18 livestock companies, decried the loss of "thousands of innocent souls ... for no clear reason" in a statement Sunday.
"We do not accept such explanations," the statement said. "We request an urgent investigation of the responsible institutions, and the punishment of those guilty according to the Romanian law of animal welfare."