The Philippines demanded Sunday that Beijing explain the presence of 10 of its ships and barges near a shoal in the disputed South China Sea amid concerns China was preparing new construction in the area.
Six of the vessels near the Scarborough Shoal were coastguard ships, while four looked like barges and two were troop ships, Defence Secretary Delfin Lorenzana said.
"No dredging work has been seen," Lorenzana said. "However, the presence of so many ships, other than the coastguard, in the area is cause for grave concern," he continued, adding the Foreign Ministry had been in touch with the Chinese ambassador to Manila.
"If they try to construct anything in Scarborough, it will have far reaching adverse effect on the security situation" in the region, he said.
President Rodrigo Duterte first raised concern over new construction in the disputed sea on Friday after he received reports from the Philippine coastguard of the presence of Chinese ships.
On July 12, the Permanent Court of Arbitration in The Hauge ruled that Beijing had no legal right to claim a large swathe of the area, in a case brought by the Philippines.
Manila filed the case in January 2013 after China took control of Scarborough Shoal, 124 nautical miles from the Philippines' north-western coast.
China, which did not participate in the arbitration case, has rejected the court's ruling as “null and void.”
Brunei, Malaysia, Taiwan, and Vietnam also have overlapping claims to the South China Sea, in addition to China and the Philippines.