The high seas cat-and-mouse game on Tuesday followed assurances from Chinese coast guard vessels patrolling the waters that Philippine boats would be allowed to deliver provisions to the remote outpost on Second Thomas Shoal "in the spirit of humanism".

But, the Chinese radio operator warned, the two Philippine coast guard vessels escorting the two boats carrying supplies for Filipino marines stationed on a crumbling navy ship grounded atop the reef should leave or "bear full responsibility for all the consequences".

A team of AFP journalists on board the BRP Cabra, one of the two Philippine Coast Guard vessels, watched as the Chinese vessels chased, blocked and corralled the four Philippine vessels.

One of the Chinese coast guard ships came within several metres of the Cabra.

Eventually, both supply boats reached the marooned BRP Sierra Madre and unloaded their cargo.

AFP was one of three media outlets given the rare opportunity to join the Philippine resupply mission to Second Thomas Shoal, less than three weeks after Chinese coast guard ships used water cannon against a similar resupply operation.

That incident, on August 5, prevented one of the Philippine resupply boats from unloading and sparked a diplomatic spat between Manila and Beijing.

There was widespread international criticism of the Chinese actions but Beijing defended its behaviour as "professional", and accused Manila of "illegal delivery of construction materials" to the grounded ship.

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

The Philippines, Vietnam, Malaysia and Brunei have overlapping claims to parts of the sea.

China deploys hundreds of vessels to patrol the South China Sea and its reefs and Manila says China's coast guard and navy ships routinely block or shadow Philippine boats there.

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

The Philippine Navy deliberately grounded the World War II-era BRP Sierra Madre on the reef in 1999 to check China's advance in the waters.

- 'We don't need permission' -

As this week's resupply mission got underway on Monday, Chinese vessels patrolling the South China Sea appeared to be manoeuvring into position soon after the boats left Palawan.

The Philippine coast guard vessels joined up with the two resupply boats at Sabina Shoal, claimed by Manila, on Monday evening, as more than a dozen Chinese boats, including a coast guard ship, floated nearby.

The lone Chinese coast guard vessel trailed the Philippine vessels as the resupply mission sailed through the night for the final 60-kilometre leg of their journey to Second Thomas Shoal.

It was joined by another three Chinese coast guard ships soon after daybreak on Tuesday, sailing alongside the resupply mission.

The voice of a radio operator on board one of the Chinese coast guard ships crackled over the airwaves a short time later, declaring China's "indisputable authority" over the Spratly Islands.

"In the spirit of humanism, we only permit your ship carrying food and other necessary living materials and the rotating personnel without construction materials to the illegally grounded vessel," the voice said.

Filipino troops stationed on the rusting hulk depend upon the supplies for survival.

While the latest resupply mission was successful, Philippine Coast Guard spokesman for the West Philippine Sea Commodore Jay Tarriela told reporters Wednesday that the Chinese ships, including "maritime militia", had used "a lot of dangerous manoeuvres" to harass the Philippine vessels.

He dismissed the Chinese coast guard's claims of "humanitarian consideration" in allowing the delivery of supplies.

"We don't need permission from anybody," he said.