MANILA - The Philippines is to lease from Japan five aircraft to help patrol the disputed South China Sea, President Benigno Aquino announced on Wednesday, as China expands its military presence in the region.

The Philippine military, for decades preoccupied with domestic insurgencies, has been shifting its focus to territorial defence, allocating 83 billion pesos ($1.77 billion) until 2017 to upgrade and modernise its air force and navy.

Speaking at an air base south of Manila, Aquino said he had done more to build the air force than three previous governments, increasing the number of planes and helicopters to move troops and supplies and guard maritime borders.

"All this new equipment will enhance the capability of the air force to guard our territory," Aquino said.

Allies the United States and South Korea have already offered help to bolter air capabilities and Aquino announced the arrival this year of two refurbished C130 transport planes from the United States.

"We are also leasing from Japan five TC-90 training aircraft to assist our navy in patrolling our territories, particularly in the West Philippine Sea," he said, referring to the Spratly archipelago in the South China Sea.

He did not say when the Japanese aircraft would arrive.

South Korea has supplied two light fighters and will give 10 more up to 2017, he said, adding that his government would award contracts for six close air support and two long-range patrol planes. Three air surveillance radars are also due be installed.

Already in the military's plans is the acquisition of a squadron of multi-role fighters, air-to-ground missile batteries, early warning aircraft and drones.

The Philippines has made the modernisation of its air and naval forces a priority as China deploys missiles and fighters on a number of artificial islands in the South China Sea.

China claims almost the entire South China Sea, where about $5 trillion worth of ship-borne trade passes annually. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims to parts of the sea.

Last week, the Philippines and Japan signed a deal on the transfer of military equipment and technology, a document Japan needs to allow it to export weapons and guarantee they will not be transferred to a third party.

A Philippine military spokesman, Brigadier-General Restituto Padilla, said the deal for the Japanese aircraft was being finalised.

"We are not yet aware of the actual terms and conditions of the lease agreement, including the cost and duration," he said.