HANOI, Vietnam — A multinational search by Vietnamese, Philippine and Chinese rescuers was underway on Sunday for 17 crew members missing after a cargo ship sank in bad weather off a Chinese-occupied shoal in the disputed South China Sea,

The Vietnamese cargo vessel Khoi Nguyen 18, carrying 62 people, sank late Saturday near Fiery Cross Reef, which is a Chinese-built island and a military outpost in the hotly contested Spratly Islands.

Of those on board, 45 crew members have been found and 17 others are still reported missing.

The vessel “sank while operating in bad weather conditions in the East Sea,” Foreign Ministry Spokesperson Pham Thu Hang said.

The Philippine Coast Guard said it deployed a patrol vessel and an aircraft to help search for the missing crew members after receiving a request from Vietnam. Chinese rescue ships and helicopters, along with other vessels in the area, joined the operation.

Vietnamese authorities said fishing vessels had joined the search and that the families of those on board had been notified.

Philippine Coast Guard spokesperson Commodore Noemie Cayabyab said that it was coordinating with Vietnam’s coast guard “for other operational information needed to guide the search and rescue response.”

She said the coast guard was also using a search planning system to improve the chances of locating the missing crew members and had issued a navigational warning urging ships transiting the area to keep watch and assist if it was safe to do so.

The Philippine Coast Guard said the operation was being conducted under international maritime agreements and bilateral cooperation with Vietnam.

Vietnam’s Foreign Ministry thanked China for its swift assistance and said it hoped the search would continue to find the remaining crew members.

China has become increasingly aggressive in asserting its claims in virtually the entire South China Sea, through which about $5 trillion in global trade transits each year. The sea passage is also believed to be sitting atop vast undersea deposits of oil and gas.

As well as China and the Philippines, Vietnam, Malaysia, Brunei and Taiwan also have overlapping claims in the strategic waterway.