CNN  — 

Three Filipino fishermen have died after an “unidentified commercial vessel” allegedly rammed their fishing boat near Scarborough Shoal, the Philippine coast guard said Wednesday, compounding tensions in a region of the disputed South China Sea that is already a flashpoint.

In a statement, the Philippine coast guard said it was working to confirm what type of vessel was involved in the incident but added the boat that caused the collision was “foreign”.

The maritime collision occurred around 4:20 a.m. on Monday, a crew member of FFB Dearyn, the Philippine vessel that was struck, told the coast guard, according to the statement.

Eleven crew members survived the crash and used their own service boats to reach land on Tuesday morning, carrying the dead – including the boat’s captain – to Pangasinan province in northern Luzon, the country’s largest island, the statement added.

The South China Sea is a 1.3 million-square-mile waterway that is vital to international trade, with an estimated third of global shipping worth trillions of dollars passing through each year. It’s also home to vast fertile fishing grounds upon which many lives and livelihoods depend on.

Bracketed by China and several Southeast Asian nations, parts of the sea are claimed by multiple governments, with Beijing asserting ownership over almost all of the waterway, in defiance of an international court ruling.

Over the past two decades, China has occupied a number of obscure reefs and atolls far from its shoreline across the South China Sea, building up military installations, including runways and ports.

Scarborough shoal, known as Bajo de Masinloc in the Philippines and Huangyan Island in China – is a small but strategic reef and fishing ground 130 miles (200 kilometers) west of Luzon that has been a flashpoint for tensions between Manila and Beijing.

The area has witnessed increasingly frequent run-ins between Philippine vessels and tiny wooden fishing boats against much larger Chinese coast guard ships and what Manila says are shadowy Chinese “maritime militia” fishing vessels.

In 2016, an international tribunal in The Hague ruled in favor of the Philippines in a landmark maritime dispute, which concluded that China has no legal basis to claim historic rights to the bulk of the South China Sea. Manila says Beijing has ignored the ruling.

This is a developing story. More to follow.