The Philippines has asked the US to provide military "assistance" in resupplying and rotating Manila's forces in the South China Sea because they face harassment from regional power China, a military spokesman said Thursday.

The request was made the previous day by Philippine Defence Secretary Voltaire Gazmin in a meeting with Admiral Harry Harris, head of US Pacific Command, according to Colonel Restituto Padilla.

"It was a specific request on the part of the secretary of national defence to Admiral Harris to get their assistance in... resupplying and rotating troops," Padilla told AFP.

"They just took our requests and the details still have to be discussed," Padilla said, adding that the American officer made no commitment.

Padilla said the request pertained in particular to the "West Philippine Sea", Manila's term for the South China Sea.

Harris, who oversees American forces across Asia, met Wednesday with Philippine President Benigno Aquino. On Thursday, he visited the Philippine military command on the western island of Palawan, the closest landmass to the South China Sea.

A Philippine military statement said his visit was to familiarise himself with "the situation on the ground".

In his meetings, Harris had outlined a freshly drafted Pentagon report highlighting issues in the South China Sea, Padilla said earlier.

Tensions have risen in recent years between the Philippines and China due to conflicting territorial claims over these waters, including the Spratly islands located there.

Brunei, Malaysia, Vietnam and Taiwan also have claims to parts or all of the South China Sea, which is a vital maritime route, a rich fishing ground and which may hold vast mineral resources.

In asking for US assistance, Padilla said the Philippines had faced Chinese harassment, particularly when resupplying and rotating troops based on a grounded WWII-era ship on a remote shoal in the Spratly islands.

China has also recently turned isolated rocky outcroppings in the South China Sea into artificial islands that can host military facilities.

The Philippines fears these artificial islands will be used to isolate Filipino outposts in the Spratlys.

Padilla conceded the Philippines, which has one of the weakest militaries in the region, lacked the resources to fully protect its own vessels in the area.

The Philippines has been seeking to improve its defence relations with the United States and other countries to counterbalance China's forces.