A resupply mission last Saturday couldn't unload all of its cargo after China Coast Guard ships blocked and fired water cannon at Philippine coast guard vessels and charter boats carrying food, water and fuel for Filipino troops stationed on Second Thomas Shoal.

The incident has ignited a diplomatic row between Manila and Beijing, and sparked international criticism of China's actions.

A handful of marines are based on a World War II-vintage ship called the BRP Sierra Madre, which was deliberately grounded on the submerged reef in 1999 to check China's advance in the hotly contested waters. The tiny garrison depends on regular deliveries for their survival.

One of the charter boats carrying supplies to the outpost on Saturday was prevented from reaching the shoal, while the other succeeded in unloading its cargo.

The next delivery would be "early next week hopefully, but definitely before the supply runs out. We're on the clock now," Vice Admiral Alberto Carlos, chief of the Western Command of the Armed Forces of the Philippines on Palawan island, told reporters.

Carlos said they would use the same charter boats as last Saturday, adding that he hoped there would not be another water cannoning incident.

An airdrop was also being considered, he said.

Second Thomas Shoal is about 200 kilometres (124 miles) from Palawan, and more than 1,000 kilometres from China's nearest major landmass, Hainan island.

The incident has fanned tensions between the countries, which have a long history of maritime disputes in the South China Sea.

Beijing claims almost the entire waterway, through which trillions of dollars in trade passes annually, and has ignored an international ruling that its assertion has no legal basis.

Philippine military Chief of Staff General Romeo Brawner said Thursday during a visit to the Western Command in Palawan that the country needed to boost its presence in the waters.

"We have plans to deploy more ships, even our aircraft, to be able to guard our exclusive economic zone... we really have to establish our presence in the area, it's all about numbers," Brawner said.

China deploys hundreds of vessels to patrol the South China Sea and swarm reefs.

Its coast guard and navy ships routinely block or shadow Philippine boats in the contested waters, Manila says.

Beijing has defended its actions last Saturday as "professional", and accused Manila of "illegal delivery of construction materials" to the grounded ship.

The Philippines has insisted that Second Thomas Shoal is within its exclusive economic zone, and therefore its efforts to resupply troops and repair the BRP Sierra Madre are legitimate.