Foreign Minister Julie Bishop plans to issue a "please explain" to Beijing over its massive island-building program in the South China Sea, amid fears the reclaimed structures could be militarised by the Chinese.
Ms Bishop, who left on Sunday for a visit to Japan and China, said she also planned to use her meeting with Chinese counterpart Wang Yi to urge Beijing to do more to rein in neighbouring North Korea, which launched a long-range rocket this month in defiance of international warnings.
Australia's planned new fleet of submarines and broader security matters in the region are also expected to be high on the agenda of the trip, which includes calls on Japanese Prime Minister Shinzo Abe and Chinese Premier Li Keqiang. 
The visit comes as the Turnbull government continues to weigh up whether to join the United States in so-called freedom of navigation patrols through the contested waters of the South China Sea, designed to undercut Beijing's excessive maritime claims and test previous pledges not to militarise the islands.
China has built military-grade runways and massive lighthouses on some of the artificial islands, and is working on port facilities that could berth naval ships. Beijing has consistently denied it plans to militarise the islands, but most experts say that is an obvious option available to the People's Liberation Army.
Ms Bishop said she planned to push for an explanation when she meets with Chinese Foreign Minister Wang Yi.
"The focus from my point of view will be on what China proposes to do with the structures that are there, what can we expect to see from the lighthouses and the assets that are there. That's what I'll be focussing my attention. What are they going to do with it?" 
The US has twice sailed warships past islands reclaimed by China in the South China Sea, and is looking to regional powers to join it in regular patrols as a show of unity, but most are wary it would jeopardise their economic relationship with China. Reports that India could agree to joint patrols were swiftly denied by Delhi last week.
"The onus falls back on the two treaty allies and I think Japan would be unlikely to go ahead of Australia, so the buck stops here," said Euan Graham, director of the International Security Program at the Lowy Institute.
Ms Bishop said she took at face value President Xi Jinping's insistence during a visit to Washington last year that China did not intend to militarise the islands.
When she has asked Mr Wang before about the purposed runways and other infrastructure, he had said it was for "humanitarian" operations such as search and rescue, she said.
"I've had that conversation before and this time I'd like to focus in on that because we now know what's actually built there," Ms Bishop said. "[It's] a practical, pragmatic, 'what now?' ??? I'm going to take that further if I can."
Japan is pushing the strategic value of its submarine bid which would bring two of the Asia-Pacific region's leading liberal democracies closer together at a time of rising uncertainty caused by the flexing of China's muscle.
Ms Bishop said she did not expect a negative response from Beijing if Australia chooses Japan to partner on the submarine program, provided Canberra is "transparent" about its strategic intentions through the Defence White Paper.
"It hasn't been raised with me at all. I wouldn't expect China to interfere in something like that, just as we wouldn't comment if it were a Chinese tender."
Ms Bishop said she also planned to raise the need for Beijing to do more to rein in its troublesome ally North Korea, which has set the world's teeth on edge yet again in recent months with nuclear and long-range rocket tests.
"The fact is China is their closest trading partner. China provides most of their energy, most of their food," she said.
"They have a closer relationship with China than any other country. On that basis, I believe there's more China can do to try and influence to North Korea's behaviour."
Ms Bishop has a heavy schedule of meetings in coming days, with officials from what Ms Bishop called the "two north Asian giants".