Foreign and defence ministers from Japan and Australia have agreed to strengthen their security ties as China becomes more assertive in pressing its claims to contested areas in the Asia-Pacific region.
The talks held online on Wednesday were between Australian Foreign Minister Marise Payne and Defence Minister Peter Dutton, and their Japanese counterparts Toshimitsu Motegi and Nobuo Kishi.
Motegi told reporters after the online talks that the officials shared their concerns about China's activity in the East and South China seas as a challenge to the international community.
Japan regularly protests to China over its coast guard presence near the Japanese-controlled Senkaku islands, which China also claims and calls Diaoyu.
Chinese vessels routinely violate Japanese territorial waters around the islands, sometimes threatening fishing boats, Japanese officials say.
Japan and China are also in dispute over the development of undersea resources in the area.
In the South China Sea, China's sweeping territorial claims have clashed with those of its neighbours, which accuse Beijing of militarising one of the world's busiest sea lanes.
Japan and Australia, in a joint statement, expressed "serious concerns about the recent negative developments and serious incidents in the South China Sea, including continuing militarisation of disputed features, dangerous use of coast guard vessels and 'maritime militia', and efforts to disrupt other countries' resources exploitation activities".
"We reaffirmed our strong opposition to any unilateral attempts to change the status quo" by China, Motegi said.
He also said the four ministers shared "grave concern" over China's human rights abuses in Hong Kong and the western Xinjiang region, where Uighurs and other Muslim minorities live.
The statement called on China "to grant urgent, meaningful and unfettered access to Xinjiang for independent international observers including the UN high commissioner for human rights".
The meeting also reaffirmed the importance of maintaining peace and stability in the Taiwan Strait, where China has recently stepped up a campaign of pressure on the self-ruled island.
China responded that it is determined to defend its sovereignty, security and development interests.
"China has indisputable sovereignty over the South China Sea islands and their nearby waters, and over the Diaoyu Island and its affiliated islets," foreign ministry spokesman Wang Wenbin told a daily briefing in Beijing.
"Issues related to Xinjiang and Hong Kong are China's internal affairs that no foreign country should intervene. China firmly rejects Japan and Australia's efforts to smear China and interfere in China's internal affairs."
Japan and Australia are in the final stages of a defence co-operation deal that will allow the Japanese Self-Defence Force to protect Australian military assets, which will be only the second for Japan outside its alliance with the United States.
Australian Associated Press