The Philippines has deployed 800 more Marines and opened a new headquarters to guard its interests in the disputed Spratlys islands, which China also claims, a senior military official said Sunday.

Straddling vital shipping lanes and believed sitting atop vast reserves of mineral deposits, including oil, the Spratlys chain in the South China Sea has long been considered a flashpoint for conflict in the region.

Apart from the Philippines and China, the Spratlys are claimed in whole or in part by Vietnam, Brunei, Malaysia and Taiwan.

Lieutenant General Juancho Sabban, appearing to want to assuage Beijing in particular, said the deployment was only meant as a defensive measure and should not be seen as an aggressive move.

"These two battalions which arrived recently will be augmenting protection of our islands," Sabban, who heads the military garrison which has jurisdiction over the Spratlys, told AFP.

"We are just on a defensive posture and are ensuring the defence of our islands. It is better to defend than retake islands once other claimants occupy them."

He said a Marine brigade headquarters had also been created on the nearby Philippine province of Palawan, facing the South China Sea, "to provide command and control" over the forces.

The Marines will not be stationed on the Spratlys but will patrol nearby.

Sabban accused China of continually fortifying its structures on islands in the Spratlys that Beijing controls, though at present "no claimant countries have manifested any offensive action".

"We are not there to create a situation where it will lead to an accidental conflict and escalate into a regional problem," Sabban stressed.

China, which is in a dispute with Japan over islands in the East China Sea, has been accused of ramping up tensions in the South China Sea. The Philippines and Vietnam over the past year raised alarm over Beijing's assertiveness.

China claims all of the South China Sea, which Manila calls the West Philippine Sea, even waters close to its Asian neighbours.

Sabban's announcement came just days after incoming Chinese leader Xi Jinping met a special Philippine envoy and expressed hope bilateral ties would improve.

The meeting was set months after both sides were locked in a tense standoff in Scarborough shoal, another outcrop in the South China Sea north of the Spratlys.