The Philippines' navy chief said Sunday it would hold a joint exercise with Japan in the South China Sea, but emphasised the collaboration was unrelated to China's land reclamation efforts in the disputed waters.

Two warships from the Japan Maritime Self-Defense Force (JMSDF) will take part in the exercise with a single Philippine ship after making a port call in the Philippines this month, said Vice Admiral Jesus Millan.

"This is a port call, a regular port call of the Japanese navy and while they are here, it would be good if we can practise this code of unplanned encounters at sea," he said.

The exercise will take place just outside the former US naval base of Subic, off the archipelago's west coast, he added.

The Japanese vessels would be leaving Subic while a Philippine ship was heading there under the training scenario, he said.

Millan said Japanese and Philippine sailors would have an opportunity to "compare notes" during the exercise, but stressed it had nothing to do with the Philippines' territorial dispute with China over conflicting claims to large parts of the sea.

The Philippines has been seeking closer ties with regional allies amid what it sees as Chinese aggression in pressing its territorial claims.

The regional giant claims most of the resource-rich waters, even reefs, shoals and cays close to the shores of its neighbours. The claims overlap those of Brunei, Malaysia, the Philippines, Vietnam and Taiwan.

Millan said that practising with the Japanese force would help with modernising the poorly-equipped Philippine military, one of the weakest in the region.

China and Japan have their own festering territorial row over the East China Sea including ownership of the Senkaku islands, which Beijing also claims and calls the Diaoyus.

There have been regular standoffs in the sea and air around the contested territory.

Earlier this month, Japanese and Philippine coast guards held anti-piracy drills in the Philippines, the first such joint exercise between the two countries following a brutal occupation by Japanese forces during World War II.

US officials said on Friday that China's rapid construction of artificial islands in the strategic waters amounted to 2,000 acres (800 hectares), with 75 percent of the total built in the last five months.

The US report said that at four reclamation sites China had moved from dredging operations to "infrastructure development" that could include harbours, communications and surveillance systems, logistics support and "at least one airfield".

The Philippine military has also cited escalating Chinese efforts to drive off Philippine aircraft from a disputed island garrisoned by Manila, which have sparked dangerous confrontations.

Japan in turn has called for international law to be observed in the South China Sea dispute and has previously promised to help in the modernising the Philippines' maritime assets.