An aerial photo taken though a glass window of a Philippine military plane shows the alleged on-going land reclamation by China on mischief reef in the Spratly Islands in the South China Sea, west of Palawan, Philippines, May 11, 2015. REUTERS/Ritchie B. Tongo/Pool

Armed Forces of the Philippines (AFP) Chief of Staff Gregorio Pio Catapang shows some images of the structures being built by China at the disputed islands during a news conference at the AFP headquarters in Manila April 20, 2015. Philippine President Benigno Aquino said on Friday the territorial dispute with China in the South China Sea was of concern for the world because global trade will be hit by China's reclamation. Recent satellite images show China has made rapid progress in building an airstrip suitable for military use in contested territory in the Spratly Islands and may be planning another, moves that have been greeted with concern in the United States and Asia. REUTERS/Romeo Ranoco

Filipino soldiers wave from the dilapidated Sierra Madre ship of the Philippine Navy as it is anchored near Ayungin shoal (Second Thomas Shoal) in the Spratly group of islands in the South China Sea, west of Palawan, Philippines, May 11, 2015. REUTERS/Ritchie A. Tongo/Pool 

Filipino residents and soldiers conduct a flag raising ceremony during the visit of Armed Forces of the Philippines military chief General Gregorio Catapang in Pagasa Island (Thitu Island) at the Spratly group of islands in the South China Sea, west of Palawan, Philippines, May 11, 2015. REUTERS/Ritchie A. Tongo/Pool 

A ship (top) of Chinese Coast Guard is seen near a ship of Vietnam Marine Guard in the South China Sea, about 210 km (130 miles) off shore of Vietnam May 14, 2014. Vietnamese ships were followed by Chinese vessels as they neared China's oil rig in disputed waters in the South China Sea on Wednesday, Vietnam's Coast Guard said. Vietnam has condemned as illegal the operation of a Chinese deepwater drilling rig in what Vietnam says is its territorial water in the South China Sea and has told China's state-run oil company to remove it. China has said the rig was operating completely within its waters. REUTERS/Nguyen Minh (POLITICS MARITIME ENERGY) 

Philippine Foreign Secretary Albert Del Rosario points to an ancient map on display at a Catholic university in Manila September 11, 2014. The Philippines on Thursday put on display dozens of ancient maps which officials said showed that China's territorial claims over the South China Sea did not include a disputed shoal at the center of an acrimonious standoff. The Philippines is in dispute with China over parts of the South China Sea, including the Scarborough Shoal, an area believed to be rich in oil and natural gas as well as fisheries resources. REUTERS/Romeo Ranoco (PHILIPPINES - Tags: POLITICS) 

Members of the Philippine marines are transported on a rubber boat from a patrol ship after conducting a mission on the disputed Second Thomas Shoal, part of the Spratly Islands in the South China Sea, as they make their way to a naval forces camp in Palawan province, southwest Philippines March 31, 2014. REUTERS/Erik De Castro (PHILIPPINES - Tags: POLITICS MARITIME MILITARY) 

A Philippine Navy personnel stands in front of an Agusta Westland AW109 helicopter before it takes off during Cooperation Afloat Readiness and Training (CARAT) Philippines 2014, a U.S.-Philippines military exercise, aboard Philippine Navy vessel BRP Ramon Alcaraz in the South China Sea near waters claimed by China June 28, 2014. Philippine and American troops are holding naval exercises this month near a disputed shoal, which will almost certainly anger China with tension already high in the South China Sea. REUTERS/Noel Celis/Pool (MID-SEA - Tags: POLITICS MILITARY MARITIME) 

The BRP Sierra Madre, a marooned transport ship which Philippine Marines live on as a military outpost, is pictured in the disputed Second Thomas Shoal, part of the Spratly Islands in the South China Sea March 30, 2014. The Philippine government vessel made a dash for shallow waters around the disputed reef in the South China Sea on Saturday, evading two Chinese coastguard ships trying to block its path to deliver food, water and fresh troops to a military outpost on the shoal. There, around eight Filipino soldiers live for three months at a time in harsh conditions on a reef that Manila says is within its 200-nautical mile exclusive economic zone (EEZ). China, which claims 90 percent of the South China Sea, says the shoal is part of its territory. Filipino troops on the civilian vessel clapped as they came within a few metres of the marooned transport ship, the BRP Sierra Madre. Supplies of food and water were then hauled up to troops onboard. REUTERS/Erik De Castro (MID-SEA - Tags: MARITIME MILITARY POLITICS) 

A Chinese Coast Guard vessel manoeuvres to block a Philippine government supply ship with members of the media aboard at the disputed Second Thomas Shoal, part of the Spratly Islands, in the South China Sea March 29, 2014. According to local media, two Chinese Coast Guard vessels on Saturday tried to block the Philippine government civilian ship from bringing troops and supplies to the military detachment stationed aboard BRP Sierra Madre. BRP Sierra Madre has been aground on the disputed shoal, which is known as the Ren'ai reef in China and the Ayungin Shoal in the Philippines, since 1999. REUTERS/Erik De Castro (PHILIPPINES - Tags: MARITIME MILITARY POLITICS MEDIA) 

A Philippine national flag flutters in the wind aboard the BRP Sierra Madre, run aground on the disputed Second Thomas Shoal, part of the Spratly Islands, in the South China Sea March 29, 2014. According to local media, two Chinese Coast Guard vessels on Saturday tried to block a Philippine government civilian ship from bringing troops and supplies to the military detachment. BRP Sierra Madre has been aground on the disputed shoal, which is known as the Ren'ai reef in China and the Ayungin Shoal in the Philippines, since 1999. REUTERS/Erik De Castro (PHILIPPINES - Tags: POLITICS MARITIME MILITARY) 

Men, on a small boat, inspect their fishnet in front of one of the two Vietnam Russian-built missile-guided frigates docked at a bay in Manila November 25, 2014. Vietnam on Tuesday showed off its two most powerful warships in the first-ever port call to the Philippines but an official said it was not trying to challenge China's superior naval forces amid tension in the South China Sea. Hanoi invited the diplomatic community to its Russian-built missile-guided frigates docked in Manila Bay at the start of a three-day goodwill visit. China lays claim to almost all of the entire South China Sea, believed to be rich minerals and oil-and-gas deposits. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also have claims, creating one of Asia's biggest possible flashpoints. REUTERS/Romeo Ranoco (PHILIPPINES - Tags: POLITICS MILITARY) 

A ship (top) of Chinese Coast Guard is seen near a ship of Vietnam Marine Guard in the South China Sea, about 210 km (130 miles) off shore of Vietnam May 14, 2014. Vietnamese ships were followed by Chinese vessels as they neared China's oil rig in disputed waters in the South China Sea on Wednesday, Vietnam's Coast Guard said. Vietnam has condemned as illegal the operation of a Chinese deepwater drilling rig in what Vietnam says is its territorial water in the South China Sea and has told China's state-run oil company to remove it. China has said the rig was operating completely within its waters. REUTERS/Nguyen Minh (POLITICS MARITIME ENERGY) 

Philippine marines of 12th Marines Regiment take part in the Cooperation Afloat Readiness and Training (CARAT) Philippines 2014, a U.S.-Philippines military exercise, on a beach facing South China sea, at San Antonio, Zambales north of Manila June 30, 2014. REUTERS/Erik De Castro (PHILIPPINES - Tags: POLITICS MILITARY) 

A Chinese Coast Guard vessel (R) passes near the Chinese oil rig, Haiyang Shi You 981 (L) in the South China Sea, about 210 km (130 miles) from the coast of Vietnam June 13, 2014. The Philippines said on Monday that China's "expansion agenda" in the disputed South China Sea threatened security and stability in the region, calling on all claimant states to halt construction activities that may raise tensions. Picture taken on June 13, 2014. REUTERS/Nguyen Minh (MID-SEA - Tags: POLITICS MARITIME ENERGY) 

Crew members onboard a Chinese coast guard vessel are pictured on the South China Sea, about 210 km (130 miles) offshore of Vietnam May 14, 2014 Anti-China violence subsided in Vietnam on Friday after the prime minister called for calm, but the United States said China's "provocative" actions in maritime disputes were dangerous and had to stop. Thousands of people attacked businesses and factories in Vietnam's industrial parks earlier in the week, targeting Chinese workers and Chinese-owned businesses after Beijing parked an oil rig in a part of the South China Sea claimed by Hanoi. Many Taiwanese-owned firms bore the brunt because the crowds believed they were owned by mainland Chinese. Picture taken May 14, 2014. REUTERS/Nguyen Minh (MID-SEA - Tags: POLITICS CIVIL UNREST SOCIETY MARITIME)