The Philippines, Canada, United States and Australia kicked off their first joint military exercise on Wednesday in the South China Sea to enhance inter-operability among their forces, the four countries' military said, Paralel.Az reports citing Reuters.

The two-day exercise, which will involve naval and air force units, is the first among the four countries, and follows the first Philippines-Japan joint exercise in the disputed South China Sea last week.

The United States, a treaty ally of the Philippines, has held similar exercises with other countries in the disputed waterway, having carried out drills with Manila and Japan in June.

The four nations said in a statement that they uphold the right to freedom of navigation and overflight of the South China Sea, adding that naval and air force units will operate together in Manila's 200-nautical mile exclusive economic zone to improve cooperation and interoperability.

"We stand together to address common maritime challenges and underscore our shared dedication to upholding international law and the rules-based order," the statement read.

China claims as its territory much of the South China Sea, a conduit for roughly $3 trillion in annual ship-borne trade, despite competing claims by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Manila and Beijing have repeatedly clashed in the South China Sea, accusing each other of aggressive behaviour involving their ships and of damaging the marine environment.

In 2016, the Permanent Court of Arbitration in The Hague said China's claims had no legal basis, a decision Beijing has rejected.

China's embassy in Manila did not immediately respond to a request for comment on the four nations exercise.