The United States and the Philippines kicked off joint naval exercises Thursday in the South China Sea near waters claimed by Beijing, amid tense territorial rows between China and its neighbours.

Filipino military officials said the week-long manoeuvres, involving three US warships and more than a thousand servicemen, would address Manila's "capability gaps" as well as testing its newest military vessels.

The Philippines is engaged in a bitter territorial dispute with China over parts of the South China Sea, which Beijing claims almost in its entirety.

China has increasingly asserted its claims to the sea, which are believed to harbour vast oil and gas deposits, and parts of which are also claimed by Vietnam, Malaysia, Brunei and Taiwan. Beijing placed an oil rig in disputed waters last month, sparking deadly anti-China riots in Vietnam.

Philippine officers said the annual war games, involving more than a thousand US personnel and about 400 Filipino counterparts, would test the Philippines' two newest warships -- a pair of decommissioned US coastguard cutters that were reconfigured into frigates.

"We committed two of our relatively new ships to participate in this exercise because we really wanted these ships to become proficient in what they do," fleet commander Jaime Bernardino told reporters.

"We wanted them to become proficient in firing their guns and all the things they do on the ground."

He added that the Philippines' territorial waters are "very porous" to foreign vessels.

"These are the gaps that we would like to address -- make sure we detect (foreign vessels) properly, we intercept them and we neutralise them if necessary."

But he added that simulated boardings being carried out as part of the exercises have not been planned with any specific country in mind.

Two warships were docked at Subic Bay for the drills -- a few hours' sailing distance from Scarborough Shoal, a South China Sea outcrop that was effectively taken over by China after a tense stand-off with the Philippines in 2012.

Rear Admiral Stuart Munch, commander of a Pacific-theatre US submarine force, said the annual exercises were "designed to improve our inter-operability and build our relationship," so that the two navies can support each other better in more complex operations.

Manila, which has one of the weakest militaries in the region, has been increasingly turning to its main defence ally Washington to back it up against China.

It recently signed a new defence accord with its former colonial power giving US forces greater access to Filipino bases.

Although the United States has taken no side in the territorial disputes, it has warned China against taking "destabilising actions" in the South China Sea.