Philippines Marines and a television reporter on board a supply ship gesture towards a Chinese coastguard vessel near Second Thomas Shoal in the South China Sea on March 29.

Philippines Marines and a television reporter on board a supply ship gesture towards a Chinese coastguard vessel near Second Thomas Shoal in the South China Sea on March 29. Photo: Reuters

One day after a Philippine government vessel succesfully ran a Chinese blockade to deliver supplies and fresh troops to its military outpost in the South China Sea,  Manila has challenged Beijing's claims to the disputed waters at a United Nations tribunal.

The South-east Asian nation asked the UN's Permanent Court of Arbitration in The Hague to uphold its right to exploit waters within its 200-nautical mile exclusive economic zone under the United Nations Convention on the Law of the Sea. The arbitration pleading, almost 4000 pages long, was submitted electronically on Sunday.

"It is about defending what is legitimately ours," Foreign Affairs Secretary Albert del Rosario said in Manila. "It is about guaranteeing freedom of navigation for all nations. It is about helping preserve regional peace, security and stability."

The BRP Sierra Madre, which was deliberately run aground near Second Thomas Shoal in 1999 to serve as a Philippines military outpost.

The BRP Sierra Madre, which was deliberately run aground near Second Thomas Shoal in 1999 to serve as a Philippines military outpost. Photo: AP

The latest move  comes as Philippines President Benigno Aquino negotiates a defence pact that would let the US boost its troop presence in the Philippines and build facilities inside military bases there. The Philippines lacks the military muscle to thwart China, which has a defence budget 47 times that of the Philippines.  

"The case could further heighten tensions and prompt China to move to shoals claimed by the Philippines," said Ramon Casiple, executive director of the Institute for Political and Electoral Reform in Manila. "Other claimant nations such as Vietnam, Brunei and Malaysia are watching how this case will play out."

The cat-and-mouse encounter on Saturday, witnessed by media invited on board the Philippine ship, offered a rare glimpse into the tensions playing out routinely in  one of the region's biggest flashpoints.

Philippines Marines load supplies onto the Sierra Madre after the supply vessel successfully ran China's attempted blockade.

Philippines Marines load supplies onto the Sierra Madre after the supply vessel successfully ran China's attempted blockade. Photo: AP

"If we didn't change direction, if we didn't change course, then we would have collided with them," Ferdinand Gato, captain of the Philippine vessel, a civilian craft, told Reuters after his boat had anchored on the disputed Second Thomas Shoal.

The outpost is a huge, rusting World War II transport vessel that the Philippine navy intentionally ran aground in 1999 to mark its claim to the reef.

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 per cent of the South China Sea, says the shoal is part of its territory.

Philippines Marines salute their country's flag after the changing of the guard on board the Sierra Madre.

Philippines Marines salute their country's flag after the changing of the guard on board the Sierra Madre. Photo: AP

Things were going smoothly for the Philippine ship until it was spotted by a Chinese coastguard ship about an hour away from the Second Thomas Shoal. The Chinese boat picked up speed to come near the left of the white Philippine ship, honking its horn at least three times.

The Chinese ship slowed down after a few minutes, but then a bigger coastguard vessel emerged, moving fast to cut the path of the Philippine boat.

The Chinese sent a radio message to the Filipinos, saying they were entering Chinese territory.

"We order you to stop immediately, stop all illegal activities and leave," said the radio message, delivered in English. Captain Gato replied that his mission was to deliver provisions to Philippine troops stationed in the area.

The Philippine vessel eventually manoeuvred away from the Chinese, entering waters that were too shallow for the bigger coastguard ships.

A US navy plane, a Philippine military aircraft and a Chinese plane, all visible from their markings, flew above the ships at different intervals.

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.

Later, the eight soldiers due to be relieved put on military fatigues for a daily ceremony to lower the Philippine flag at dusk.

"What we want to accomplish is for this area to remain ours. This is the one thing that we are guarding here," said sergeant Jerry Fuentes, a Philippine marine set to deploy on the BRP Sierra Madre.

China's Foreign Ministry said late on Saturday that the action by the Philippines would not change the reality of China's sovereignty over the shoal, which Beijing calls Ren'ai reef.

"China will never tolerate the Philippines' occupation of the Ren'ai reef in any form," it said.

Reuters, Bloomberg