About 250 Filipinos live on Thitu Island, the largest and most inhabited island of the Spratlys, in the South China Sea. But Chinese ships are never far away.

While visiting the Philippines, Harris is making a stop at Palawan, an island bordering the South China Sea, where there have been ongoing territorial disputes between China and its neighbors.

Manila says 220 fishing vessels believed to be manned by China's maritime militia were observed anchored side by side at the disputed Whitsun Reef earlier this month.

The move appears to be a show of strength meant to signal the new administration's determination to stand firm against China's steady encroachment in the strategic waterway.