The Philippines is to hold simultaneous naval drills next week with key allies the United States and Japan, the military said Thursday, as Chinese building continues on the disputed South China Sea reefs.

The annual joint manoeuvres with the United States will include a P3-Orion spy plane flight and a helicopter crash and rescue simulation near disputed waters, officials said.

The exercises with the Japanese Maritime Self-Defence Force, only the second ever, will be staged separately, but in the same week as the US exercise, Philippine navy spokesman Commander Lued Lincuna said.

Lincuna could not immediately provide details of the second exercise but Japanese media, quoting unnamed official sources, said it would be staged in the South China Sea.

The Japanese media also said Japan would field a P3 surveillance aircraft.

"The joint training will help capacitate and familiarise our troops with modern equipment. There will be sharing of information, techniques and best practices on the tactical level," Lincuna told AFP.

He said the twin joint manoeuvres were not directed against China, which has built artificial islands on South China Sea reefs claimed by the Philippines.

"They are regularly planned and scheduled exercises. With Japan, the focus is on search and rescue and disaster relief," Philippine foreign affairs spokesman Charles Jose told AFP.

The US joint manoeuvres, Lincuna said, would be held near the island of Palawan, though off the eastern coast rather than the South China Sea-facing west.

The Philippines held landmark naval exercises with its World War II foe Japan only last month on the South China Sea, less than 300 kilometres (186 miles) from a Philippine-claimed shoal now under Chinese control.

The United States is the Philippines' longest-standing military ally, with the two countries bound by a 64-year-old mutual defence treaty and a separate visiting forces agreement.

An agreement that would allow the US to rotate more troops in Philippine military bases was signed last year, but will not be implemented until the Supreme Court decides on its legality.

Earlier this month, President Benigno Aquino and Japanese Prime Minister Shinzo Abe agreed to start negotiations for the transfer of defence equipment, including anti-submarine reconnaissance aircraft and radar technology.

China said on Tuesday that land reclamation in the disputed Spratly islands would finish soon but be followed by "facility construction", as it reasserted its claim over almost the entire South China Sea.

Philippine military surveillance revealed that a giant runway on one of the reefs was "75-percent complete", potentially giving Beijing longer military reach, defence department spokesman Peter Galvez had said.

China is separately engaged in a long-standing dispute with Japan over an island chain in the East Sea.

China's claims in the South China Sea overlap with those of the Philippines, Vietnam, Malaysia and Brunei.

The Philippines has challenged China's claims before a United Nations-backed arbitration tribunal, where it is expected to argue its case at the court's first hearing next month.

China has refused to participate in the arbitration.