TOKYO Foreign ministers from Australia, India, Japan and the United States said on Monday that they were seriously concerned about intimidating and dangerous manoeuvres in the South China Sea, and pledged to bolster maritime security in the region.

The joint statement came after talks between the so-called "Quad" countries in Tokyo, attended by Australia's Penny Wong, India's Subrahmanyam Jaishankar, Japan's Yoko Kamikawa and Antony Blinken from the US.

In security talks between the US and Japan on Sunday, the two allies labelled China as the "greatest strategic challenge" facing the region.

"We are seriously concerned about the situation in the East and South China Seas, and reiterate our strong opposition to any unilateral actions that seek to change the status quo by force or coercion," the ministers said in the statement, which did not directly mention China.

They also expressed serious concern about the militarisation of disputed features, and coercive and intimidating manoeuvres in the South China Sea, including dangerous use of coast guard and maritime militia vessels.

Chinese vessels have repeatedly clashed with Philippine ships seeking to resupply its troops on the disputed Second Thomas Shoal in recent months, although the two countries in July reached a provisional agreement that aims to ease tensions.

The Quad group said they were working on a series of initiatives to maintain "the free and open maritime order", including helping partners improve domain awareness via satellite data, training and capacity building. They also announced a plan to set up a new maritime legal dialogue.

"We are charting a course for a more secure and open Indo-Pacific and Indian Ocean region by bolstering maritime security," Blinken said in remarks to reporters after the meeting.

"In practical terms what does this mean? It means strengthening the capacity of partners across the region to know what's happening in their own waters," he added.

He said the US would continue to work with its partners to ensure freedom of navigation and the unimpeded flow of lawful maritime commerce.

The US announced plans on Sunday for a major revamp of its military command in Japan. It was among several measures announced by the allies to address what they said was an "evolving security environment", noting various threats from China including its muscular maritime activities.

"Uncertainty surrounding the international order. as well as the international situation, has been increasing with Russia continuing its aggression in Ukraine, attempts to unilaterally change the status quo by force in the East China Sea and South China Sea, and the launch of ballistic missiles by North Korea," Japan's Kamikawa said after the talks.

The Quad ministers also pledged to advance cooperation in cybersecurity, to protect supply chains and critical infrastructure, including undersea cables.

After leaving Tokyo, Blinken and US Defense Secretary Lloyd Austin will hold security talks with another Asian ally, the Philippines, as US President Joe Biden's administration seeks to counter an increasingly bold China.

  - Reuters