The Philippines wants to acquire two more navy ships from the United States to boost its maritime protection amid threats from China, the country's military chief said Wednesday.

The new acquisitions would come under the fresh US military assistance announced by US Secretary of State John Kerry when he visited the Philippines last month, armed forces chief of staff General Emmanuel Bautista said.

"Within the last year, we realised that there is a real threat out there in terms of securing, defending our territory," Bautista told ANC television.

He said that ideally the country needed about six more frigates to guard its long coastline effectively.

"In fact, we are bidding now for two frigates, hopefully we will be able to acquire them in (a) couple of years," Bautista said.

He said he has made "maritime domain awareness" and protection a key concern of his leadership.

The funds used to boost maritime defence, he said, would come from the $40 million military assistance pledged by Kerry in December.

The Philippines has already acquired two refurbished American frigates in the past two years, and they now lead patrols in the South China Sea.

The Philippines, a long-time US military ally, has been locked in an increasingly tense standoff with China involving disputed reefs and islands in an area Manila calls the West Philippine Sea.

In 2012, the flagship BRP Gregorio del Pilar, the first acquired from the US, confronted Chinese ships on Scarborough Shoal, a small outcrop just off the coast of the country's main island of Luzon.

The Chinese eventually gained control of the outcrop after Manila backed down. However, the government sought UN arbitration to settle the dispute, a move rejected by China.

Manila has also increasingly looked to the US for help, and negotiations are ongoing for an increased rotational presence of American soldiers in the Philippines as part of Washington's "pivot" to Asia.

Bautista said the Gregorio del Pilar, as well as another frigate that arrived last year, have been deployed to protect the country's waters.

"There are Chinese fishing vessels in the West Philippine Sea as we speak," he said, but declined to say where they were in the disputed waters.

China claims nearly all of the South China Sea, including waters near the coast of its neighbours.

Recently, it has declared an "air defence identification zone" over the East China Sea where it is engaged in a dispute with Japan.

Kerry has warned China against imposing a similar restriction over the South China Sea, and said the US government also rejected the zone over the East China Sea.

Last week China also announced a new fisheries law requiring foreign vessels to seek permits for activities in much of the South China Sea, in another move that triggered angry protests from Manila.