A flotilla of small wooden fishing boats had also joined the initial stages of the voyage to help distribute food packs and fuel after setting off from the western province of Zambales.

The activists were heading to assert Manila's sovereignty over the Scarborough Shoal and surrounding waters - which is claimed and guarded by China.

Two weeks ago, Chinese coastguard and suspected militia ships damaged patrol and fishing vessels from the Philippines with the use of water cannons.

The activists, who belong to a non-government coalition called Atin Ito - This Is Ours - said they would seek to avoid confrontation but were prepared for any outcome.

Organiser Rafaela David said: "Our mission is peaceful based on international law and aimed at asserting our sovereign rights."

China repeated its claim on Wednesday that it has indisputable sovereignty over the shoal which it calls Huangyan Island.

Foreign ministry spokesperson Wang Wenbin said: "If the Philippine side abuses China's goodwill and infringes on China's territorial sovereignty and jurisdiction, China will defend its rights in accordance with the law.

"The relevant responsibilities and consequences are entirely borne by the Philippine side."

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The increasing frequency of the clashes between the Philippines and China has left some Filipino navy personnel injured and has damaged supply boats in recent months.

It continues to spark fears the territorial disputes in the waters could degenerate into an armed conflict between China and the US, an ally of the Philippines.

In 2012, China seized the Scarborough Shoal, which has a vast fishing lagoon ringed by mostly submerged coral formations, by surrounding it with its coastguard ships after a tense standoff with Philippine government ships.

The Philippine government brought the disputes to international arbitration in 2013 and mostly won with a tribunal in The Hague.

The ruling declared the Scarborough Shoal a traditional fishing area for Chinese, Filipino and Vietnamese fishermen - but China rejected the outcome and continues to ignore it.