Thousands of US and Filipino troops began annual military exercises on Friday that the Philippines said were vital to building its defence capabilities to face the rising threat of China.

Philippine Foreign Secretary Albert del Rosario used the launch of the 12-day Balikatan manoeuvres to accuse China of destabilising Asia with aggressive and illegal actions in the South China Sea.

"For our region excessive and exaggerated maritime and territorial claims have not only created uncertainty but have undermined the rule of law," del Rosario said in a speech at the nation's military headquarters in Manila.

"Regional peace and stability have been placed at serious risk."

Del Rosario later said he was referring specifically to China.

China claims most of the South China Sea, including waters and tiny rock outcrops near the coasts of smaller neighbours such as the Philippines.

Tensions have escalated in recent years as China has sought to stamp its authority over the region.

The Philippines has accused China of occupying a shoal close to its main island, and appealed to the United Nations to rule on the validity of Chinese claims to the resource-rich sea.

And last month China's navy began patrolling disputed waters, sending vessels to within 80 kilometres (50 miles) of the Malaysian coast and at one point firing "warning signal shells" at a Vietnamese boat.

Amid the rising tensions, the Philippines has sought closer diplomatic and military ties with the United States, its former colonial ruler.

The two countries share a 61-year-old mutual defence pact, which requires the United States to come to the aid of the Philippines if it is attacked.

Del Rosario said the Balikatan (shoulder-to-shoulder) exercises were a very important part of the Philippines' efforts to secure US support.

"For my country we need to secure our borders and protect our territorial integrity more vigorously than we have before," he said.

"Balikatan... is an important contribution in not only preparing both our armed forces to work together but also in building my country's own capacity to defend itself."

The manoeuvres involve more than 8,000 US and Filipino troops, 30 military aircraft including a dozen US F/A-18 Hornets and three naval vessels, the two countries said.

Friday's launch only involved speeches from military and political leaders from the two sides.

The media will be allowed access to exercises next week, some of which will involve combat drills and simulated rescue work for natural disasters.

Del Rosario also said it was vital for the Philippines to have more US forces rotate throughout the year, and not just for scheduled exercises such as Balikatan.

"This will be crucial in our efforts in the short term to establish our minimum credible defence posture, and in the long term to build a more robust national defence structure," he said, without giving details.

The Philippines said last year it would allow more US troops to visit for short durations, such as for naval port calls, although it ruled out a return of permanent bases.