Nine hungry marines guarding the Philippines' loneliest outpost aboard a rusted World War II vessel had just one option after Chinese vessels blocked fresh supplies from reaching them -- go fishing.

The troops were 200 kilometres (120 miles) from the nearest major Philippine island, holding on to a tiny reef in the South China Sea as part of a decades-long territorial row that in recent months had grown increasingly hostile.

"We knew about the dangers signing on to the job, but my worry was we were running out of supplies," Mike Pelotera, the leader of the Marine unit, told AFP after his five-month mission ended this week and he returned to shore.

"But we are marines and we adapt, we went fishing."

In a remarkable act of military doggedness, the Philippines has since 1999 stationed a tiny number of marines on a former US Navy boat that was deliberately grounded on a group of islets and reefs called Second Thomas Shoal.

The 100-metre (328-foot) BRP Sierra Madre, built during World War II then acquired by the Philippines in the 1970s, is now little more than a rusted hull and incapable of sailing.

But it has thwarted Chinese efforts to occupy all of the area, which is believed to contain huge deposits of oil and gas.

The Philippines grounded the boat at the tiny shoal in response to China's military occupying Mischief Reef, about 40 kilometres miles away, in 1995.

Both are within the Philippines' internationally recognised exclusive economic zone, and roughly 1,100 kilometres from the nearest major Chinese landmass.

But China claims nearly all of the South China Sea, even waters close to the coasts of the Philippines, Vietnam, Brunei and Malaysia. Taiwan has a similarly large claim to China.

The competing claims have made the sea, which is also home to some of the world's busiest shipping lanes, a potential trigger for major military conflict.

Dozens of Vietnamese soldiers died in losing battles in 1974 and 1988 with Chinese forces for control of the Paracel islands in the sea's north.

- China increases pressure -

China had largely tolerated the Philippines' plucky effort to hold on to Second Thomas Shoal in the Spratlys archipelago to the south, but last year began increasing pressure to end what it termed an "illegal occupation".

In May the Philippines said a Chinese warship had begun "provocatively" circling the Sierra Madre, and lodged a formal protest.

Since then, the Philippine military has reported a near constant presence of Chinese vessels encircling the marines.

However China had always allowed the Philippine vessels to sail up to the reef and deliver new supplies to the marines, who generally do tours of duty lasting between three to six months.

This changed last month when vessels marked "China Coast Guard" blocked two civilian resupply boats, forcing Pelotera and his men to cast their fishing lines into the sea.

The marines said they were relieved a few days later to see a tiny twin-propeller Philippine military plane fly low and drop sacks of food near the boat.

Some of the marines jumped into the water and swam out to collect the bags. They filmed the joyous moment and the military this week released that footage, as well as clips of the initial blockade, to AFP.

"We were happy when the plane dropped the supplies... we were good for another few weeks," a heavily bearded and deeply tanned Pelotera said.

"But we were also worried because we knew the Chinese ships were still around."

The Philippine military sent another civilian vessel last weekend with a fresh batch of marines to rotate with Pelotera's crew, plus many months' worth of food.

Vessels marked with "China Coast Guard" again tried to form a blockade, which was witnessed by AFP reporters flying above in a Philippine military plane.

But after a dramatic stand-off lasting two hours, the smaller Philippine boat out-manoeuvred the Chinese ships and sailed into the shallow waters of the shoal.

"Some of the troops jumped 40 feet (12 metres) from the top of the deck to the sea in celebration," Pelotera said.

"It meant we could now go home to our families, have a haircut and showers."

The Chinese government reacted with fury to the defeat, with the mood in Beijing souring further when the Philippines also appealed on the weekend to the United Nations for it to rule that China's claims to most of the sea were invalid.

China has refused to take part in any UN arbitration, saying it will only negotiate directly with rival claimants but at the same time insisting it will never concede any territory.

"The Philippines must bear all consequences for its provocations," Chinese foreign ministry spokesman Hong Lei said on Monday.

For Pelotera, 30, confronting China at sea was more daunting than other missions fighting deadly jungle battles against Islamic militants in the southern Philippines.

"Both missions are dangerous. But here, we are against a bigger enemy. And we are protecting our sovereignty, not just fighting a small group of rebels... here we are always in danger."