Japan and Australia said Wednesday they have stepped up their defence ties and moved toward a possible future submarine deal, as a rising China stirs tension in the Asia-Pacific region.

Japanese Foreign Minister Fumio Kishida and Defence Minister Itsunori Onodera met with in Tokyo with Julie Bishop and David Johnston, their respective opposite numbers, for the fifth round of so-called "2+2" talks.

The Japanese said the two sides reached a broad agreement on a legal framework to allow the two nations to conduct joint research and trade in defence equipment.

"We reached a conclusion on negotiations for an agreement on cooperation in the field of defence equipment and technology," Onodera said in a joint press conference.

He said details of the pact still needed to be ironed out.

But Bishop stressed that Japan and Australia are "natural partners" who are developing their "strong relationship" into a "special relationship."

Johnston said Australia was particularly interested in Japanese diesel-electric submarines, although he added that Canberra has also approached other partner nations to study their submarine technologies.

Following an Australian request, Johnston will be given an extensive look at Japanese submarines during his stay.

Australia needs to replace its fleet of stealth subs over the coming years at a reported cost of up to US$37 billion.

- Japan defence boost -

The potential deal between the two nations could boost Japan's defence industry, while also further cementing relations both economically and militarily.

Onodera also said the two nations are looking to boost the interoperability of their troops through more joint drills, humanitarian assistance programmes, disaster relief and projects to ensure maritime security.

The ministers agreed on joint basic research for marine hydrodynamics to be applied for construction of future military vessels and submarines.

The four ministers followed up on a free trade pact and a security deal reached in April between Australian Prime Minister Tony Abbott and his Japanese counterpart Shinzo Abe, who will visit Australia next month, Bishop said.

Abe has argued that Japan must play a bigger role on the global stage and has pushed to loosen restrictions on when its well-equipped armed forces can act.

He has also relaxed a self-imposed ban on weapons exports, paving the way for the possible deal with Australia.

The ministers voiced their rejection of "the use of force or coercion to unilaterally alter the status quo in the East China Sea and the South China Sea" in an apparent reference to China's increasingly aggressive territorial claims.

Beijing has intensified its claims over the South China Sea, and has butted heads with Hanoi and Manila.

Japan's ties with China have remained sour, due mainly to a territorial dispute in the East China Sea.

Worries about China have encouraged a relationship-building drive across Asia, analysts say, with Australia and Japan a notable pairing.

In a stark reminder of the possible risks posed by the tense relationship in East Asia, Japan on Wednesday said Chinese fighter jets had flown "dangerously" close to two of its military planes in the East China Sea.

Two Chinese SU-27 jets flew as close as 30 metres (100 feet) away from the Japanese defence aircraft Onodera told reporters, adding his ministry had lodged a diplomatic complaint.

The alleged incident -- the second in less than three weeks -- occurred over the open seas but in an area where the two countries' air defence identification zones overlap.

Observers warn that such actions by high-speed aircraft could easily result in an accident, which could rapidly spiral into a confrontation.