A Hong Kong cargo ship carrying 22 people has sunk in international waters off South Korea and Japan, coastguard officials say. Japan's coastguard said on Wednesday it had rescued four crew members from a cargo ship that sank overnight off the country's southwest, but was still searching for 18 others. Meanwhile, South Korean authorities said they received a distress signal from the 6,551-ton ship carrying lumber at around 1:47 am, 148.2 kilometres southeast of the city of Seogwipo on Jeju island.