MANILA - Apart from asserting their historical rights based on the nine-dash line, China is keen on reclaiming the Scarborough Shoal due to its strategic position in the Pacific region, Supreme Court Senior Associate Justice Antonio Carpio said Thursday.

In an interview with ANC's Headstart, Carpio explained that the shoal, a few hundreds kilometers off Palawan, guards the exit to the Pacific where there could be a better platform than China's Hainan island should it decide to fire a missile towards the United States.

"Because the Chinese submarines, nuclear-armed submarines are based in Hainan and if they fire their missiles in the South China Sea, those missiles will not reach the US because the range is only about 7,500 kilometers," he said.

"They have to go to the mid-Pacific and their only exit is through the Basi Channel and an air and naval base of China in Scarborough Shoal will protect that exit to the Basi Channel," he added.

The Armed Forces of the Philippines (AFP) on Wednesday revealed that China has continued its expansion activities in the disputed South China Sea, with its vessels spotted even in the Philippine sea.

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It said Chinese research vessels in waters within or close to the Philippines and that Chinese fishing vessels have been increasing in number in two places, Scarborough Shoal in Zambales and Subi Reef, one of China's seven man-made islands and the one near the Philippines' Pag-asa Island.

Carpio said while the presence of Chinese warships in President Rodrigo Duterte's hometown in Davao is "normal," its presence in Scarborough Shoal is something else.

"If they have increased their presence, that means they are planning something and Scarborough Shoal, I think, is the last shoal that they will reclaim and build into an artificial island to house, to host an air and naval base. That could happen anytime," he said.

Once China has this base in Scarborough, Carpio said China's warships can then go to the Basi Channel to "protect their outlet to the Pacific."

China, a rising economic power in Asia, has long had tense relations with the United States, an ally of the Philippines, in terms of economic dominance and military influence. Though potentially adversarial, many scholars have also described their relationship as strategic.

Recently, US President Donald Trump invited Chinese President Xi Jinping to the White House in what was perceived as his administration's step back from the strong stance he took during the campaign.