Japan says Australia is not "walking alone" as it cops trade sanctions and grapples with security concerns relating to China.
Ambassador Yamagami Shingo has also emphasised the importance for both allies of ensuring the security of key shipping routes.
"The East China Sea is just as crucial for Australia's security and economic interest as the South (China Sea). Both are a lifeline for us," Mr Shingo told the National Press Club on Wednesday.
"Any unilateral attempt to challenge the status quo by force or coercion in these seas will inevitably impact upon our prosperity."
The ambassador applauded how Australia had "faced up to tremendous pressures" of China's trade sanctions on barley, beef, coal, copper, lobster, timber and wine imports.
"Australia is not walking alone. Japan fully supports Australia's efforts to solve the ongoing trade disputes through dialogue in accordance with international laws," he said.
Mr Shingo added Japan and Australia were close to finalising a formal agreement to boost military cooperation.
The leaders of both nations agreed in principal to the Reciprocal Access Agreement late last year.
Australian Associated Press