BANGKOK (AP) — Two people were dead and four others missing after a Singapore-flagged cargo ship with 21 Filipinos on board capsized in the South China Sea, Chinese authorities said Friday.

The Chinese Coast Guard and navy operations from the People’s Liberation Army’s Southern Theater Command have rescued 15 people in the ongoing operation. Among them, 14 were in stable condition, according to the PLA’s Southern Theater Command.

The boat capsized about 100 kilometers (60 miles) northwest of Scarborough Shoal, said the Chinese Coast Guard in a statement. Scarborough is one of the most disputed shoals in the South China Sea.

Contact was lost Thursday night with the cargo ship that was on its way to Guangdong province in China’s south.

The Philippines Coast Guard said in a statement Friday that they sent two vessels and aircraft to assist in rescue operations with the crew of the cargo ship it identified as the Devon Bay.

The area is the site of frequent showdowns between Chinese and Philippine ships. Both countries make claims to the territory and patrol the waters near the shoal. Vietnam, Malaysia, Brunei and Taiwan also have overlapping claims in the South China Sea.

A Chinese navy ship accidentally collided with a Chinese Coast Guard ship in August while trying to block a Philippine Coast Guard vessel near Scarborough Shoal.

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A previous version of this report incorrectly described Scarborough Shoal as claimed by Vietnam, Malaysia, Brunei and Taiwan in addition to China and the Philippines. Only China, the Philippines and Taiwan claim the Scarborough Shoal, while Vietnam, Malaysia and Brunei claim other parts of the South China Sea near their onshore territories.