Filipino doctors set sail on a medical mission to a disputed island in the South China Sea.

The team of medical practitioners boarded the B Florentino Das - a modernised 'balangay' or wooden boat used by pre-colonial Filipino seafarers - and departed Butuan City in Agusan del Norte province on May 27.

They voyaged toward Pag-asa Island in Palawan province around 750 miles away, in a 'challenging' nine-day journey marred by power outages and poor weather.

The boat safely docked on the island on June 4, with the medical mission proceeding the day after as Chinese coast guard and militia ships loomed off the coast.

Former transportation and environment undersecretary Art Valdez, who was part of the expedition, told local media: 'Our message here is humanitarian and peace, let us be reminded that Filipinos riding in a boat like this thousands of years ago have fought symbolically against all invaders.

'We show to the whole world that this boat has been plying in this waters for thousands of years… long before China tries to claim historical rights.'

Expansionist China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.

The Communist rogue state - accused of genocide for its crimes against the Uyghur population - has been steadily increasing its influence in recent years through investment in developing countries.