Japan's military may join US forces on patrol in the South China Sea, the nation's top uniformed officer said in an interview published Thursday, as Tokyo seeks a greater security role.

China's recent moves to build artificial islands have created "very serious potential concerns" for Japan, Katsutoshi Kawano, chief of the Joint Staff of the Japan Self-Defence Forces (SDF), said in an interview with the Wall Street Journal.

"We don't have any plans to conduct surveillance in the South China Sea currently but depending on the situation, I think there is a chance we could consider doing so," the admiral was quoted as saying.

Kawano did not specify what actions by China might trigger the Japanese to consider starting patrols, the journal reported, and any activity by Japan's military beyond its borders would likely raise concerns at home.

Prime Minister Shinzo Abe has pushed for what he calls a normalisation of the officially pacifist nation's military posture.

But because he was unable to muster public support to amend the pacifist constitution imposed by the United States after World War II, Abe opted instead to re-interpret it.

He wants to loosen restrictions that have bound the SDF to a narrowly defensive role for decades and proposed legislation that would allow the military greater scope to act.

This week Japan and the Philippines flew patrol planes near disputed South China Sea waters.

Beijing is reclaiming land to build islands in the South China Sea, with facilities it says will be used for both civilian and military purposes.

The sea is a busy shipping lane, where the United States says Beijing has built 2,000 acres (800 hectares) of artificial islands. China claims almost all the South China Sea.

Parts of the sea are also claimed by the Philippines, Vietnam, Malaysia and Brunei.

Kawano said he hoped to see more military cooperation with South Korea, an area that has suffered because of disagreements between Tokyo and Seoul over wartime history, the journal said.

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The two neighbours have exchanged warmer words in the past few days as they marked 50 years of ties.

"Once the relations are normalised on political levels, I believe movements will emerge on our (military) levels," Kawano was quoted as saying.

He also said Japan would also like to conduct more joint exercises with Australia and India.

Abe has long criticised what he describes as China's attempts to change the status quo by force, mindful of Japan's own territorial dispute with Beijing over islands in the East China Sea that are the destination for Chinese boats and planes.