Clinton vows support for Philippines at sea

US Secretary of State Hillary Clinton on Wednesday vowed support for the Philippines amid its high-seas territorial tensions with China, delivering her message from a US warship in Manila Bay.

Boarding the visiting USS Fitzgerald on a steamy morning, Clinton signed a declaration marking the 60th anniversary of a US security treaty with its former colony and said the alliance must meet "new challenges".

"The United States is working with our Filipino allies to ensure that we can meet threats like proliferation and terrorism, and to support the Philippines particularly in the maritime domain as you move to improve your territorial defence and interdiction capability," she said.

Clinton did not directly mention China, which the Philippines and Vietnam accuse of increasingly aggressive tactics in territorial disputes in the South China Sea.

The joint declaration marking the alliance anniversary called for "freedom of navigation, unimpeded lawful commerce and transit of people across the seas".

But Philippine Foreign Secretary Alberto Del Rosario, also speaking on the California-based USS Fitzgerald, said the statement sent a strong signal on the disputes in what he called the West Philippine Sea.

The statement "attests to the vitality of our alliance, especially at a time when the Philippines is facing challenges on its territorial integrity in the West Philippine Sea", he said.