Philippine President Benigno Aquino paid tribute Wednesday to nine Marines who stood guard over a disputed outpost in the South China Sea amid rising tensions with Beijing.

Aquino, speaking to World War II veterans, vowed to continue modernising the country's poorly equipped armed forces as it faced challenges protecting its territorial integrity.

He praised the Marines who spent five months aboard a rusted ship grounded on a reef that serves as an outpost for the Philippines in the remote Spratly islands.

"Just think of the gravity of their sacrifice," Aquino said. "For five months, their entire world revolved around the sea. They had almost no communication with their families."

"There were even times when the supplies and food they needed were blocked from reaching them."

Despite the hardship, Aquino said the Marines fulfilled their duties with "their dedication anchored on keeping watch over, and safeguarding, our territory".

"The Filipino nation salutes all of you," he said.

The nine were stationed on the Sierra Madre, a World War II-era former US Navy ship that the Philippines purposely grounded on the Second Thomas Shoal to stake its claim.

The 100-metre (328-foot) ship was left there in response to China's occupation of a nearby reef in 1995.

China previously largely tolerated the Philippine presence, but last month its vessels blocked a Filipino boat trying to take supplies to the men.

The Philippine military was forced to carry out a daring food drop using a small propeller plane.

Late last month, another supply boat was chased by two of four Chinese ships that had encircled the area. But the smaller and more agile vessel managed to evade the Chinese ships, angering Beijing.

Another group of Marines aboard the supply boat relieved the nine-member contingent.

The reefs are within the Philippines' internationally recognised exclusive economic zone, and roughly 1,100 kilometres (687 miles) from the nearest major Chinese landmass.

But China claims nearly all of the South China Sea, even waters close to the coasts of other nations.