The Philippines and Vietnam will sign a strategic partnership on Tuesday, a Filipino official said, cementing an alliance forged in the face of twin territorial rows with China.

Philippine President Benigno Aquino and visiting Vietnamese counterpart Truong Tan Sang will witness the signing of the pact, foreign affairs spokesman Charles Jose told AFP Monday.

Sang will be in Manila along with other leaders from the 21-member Asia-Pacific Economic Co-operation (APEC) group for a two-day summit meant to focus on trade starting Wednesday.

But Aquino is taking the opportunity to firm up important alliances as the Philippines looks for support in its dispute with China over competing claims to the South China Sea.

China claims nearly all of the sea, which is believed to sit atop vast oil and gas resources and is home to vital shipping routes, even waters approaching the coasts of its neighbours.

The sea's other claimants are the Philippines, Vietnam, Malaysia, Brunei and Taiwan.

The Philippines and Vietnam have in recent years been the most vocal in criticising moves by China to assert greater control over these waters.

Their shared concerns over China have brought them closer in recent years, with the imminent strategic partnership the most significant development.

Jose confirmed to AFP Tuesday's scheduled signing via a short text message, without giving further details.

But the Philippines and Vietnam had previously said the agreement would bolster defence, political and economic ties, and was being brokered with China in mind.

"We will deepen our cooperation in order to solve all the issues concerning the South China Sea," Vietnamese ambassador to the Philippines Truong Trieu Duong told reporters in September when discussing the planned partnership.

On the sidelines of APEC, Aquino is also scheduled to hold official bilateral talks with US President Barack Obama and Japanese Prime Minister Shinzo Abe.

Obama's aides have said the South China Sea would be a "central issue" during his visit to the Philippines.

Chinese President Xi Jinping is also due to arrive in Manila on Tuesday for APEC. China has insisted the row should not be a focus during the summit.

Aquino has not been able to secure a meeting with Xi, according to Philippine officials.

Obama to visit Philippine Navy flagship
Manila (AFP) Nov 16, 2015 - US President Barack Obama will on Tuesday visit the Philippine Navy's flagship, the White House said, seeking to highlight American commitment to regional maritime security.

Obama will board the US-made Gregorio del Pilar shortly after arriving in the Philippine capital of Manila for annual trade talks with Asia-Pacific leaders, including China's Xi Jinping.

"In the afternoon, the president will tour the BRP Gregorio del Pilar," a White House statement said on Monday as it detailed Obama's plans for his first of three days in Manila.

Obama's aides had earlier said the president planned an event that showcased "US maritime security assistance to the Philippines and the region".

The White House statement detailed the venue, with the frigate a symbolic choice as it was formerly a US Coast Guard cutter that was acquired by the Philippines in 2011.

Obama's move risks irking China, which is embroiled in a bitter territorial row over the South China Sea with the Philippines and some of its other Asian neighbours.

China had made clear it hoped the focus of the two-day APEC summit, which starts on Wednesday, would solely be on trade talks and not touch on the South China Sea.

But US National Security Advisor Susan Rice said in Washington last week that the South China Sea would be a "central issue" during Obama's time in Asia.

After Manila, Obama will travel to Malaysia for another regional summit.

In the same briefing as Rice, national security aide Ben Rhodes said Obama's visit to the then-unnamed maritime facility was aimed at comforting nervous Asian allies.

"Clearly, in our alliance with the Philippines and our focus in the region, we have been committed to maritime security, to principles like freedom of navigation, and to the peaceful resolution of disputes," Rhodes said.

"This event will be an opportunity for the president to showcase some of that maritime security assistance."

China claims nearly all of the South China Sea, even waters approaching the coasts of its neighbours.

China's building of artificial islands in waters close to the Philippines, a longstanding US ally, prompted the American military to recently deploy a missile destroyer and B-52 bomber planes to the area.

China regularly insists the United States has no role to play in the territorial dispute.

Washington says it takes no sides, but that freedom of navigation must be maintained in the sea, which is home to some of the world's most important shipping routes.