Authorities in the southern province of Hainan said the cargo vessel Khoi Nguyen 18, with 62 Vietnamese nationals aboard, ran into distress in waters near Fiery Cross Reef, China's state broadcaster CCTV said.
A distress flare from the vessel was first spotted by a Chinese rescue ship, the Nanhai Jiu 115, on Saturday evening, CCTV said.
Six Chinese vessels, a rescue helicopter, and a Vietnamese vessel joined the search and rescue effort at the site, it said.
The Vietnamese-registered vessel is nearly 70 metres long with a gross tonnage of 999 tonnes.
The area around the reef is part of the disputed Spratly Islands, which China calls the Nansha Islands, a group of highly contested reefs, islets, and atolls in the resource-rich South China Sea.
China claims sovereignty over almost the entire strategic waterway, including the Spratlys, where it has built runways and militarised artificial islands.
But Beijing's sweeping claims overlap with those of Vietnam, the Philippines, Taiwan, Malaysia, and Brunei.
13°C