The Reciprocal Access Agreement strengthens defence ties between the two U.S. allies at a time when China is asserting its role in the region and the United States is going through a messy leadership transition.

The pact allows Japanese and Australian troops to visit each other's countries and conduct training and joint operations and was agreed in principle by Japanese Prime Minister Yoshihide Suga and his Australian counterpart, Scott Morrison, who is visiting Tokyo.

"I hereby announce that we reached agreement in principle on a reciprocal access agreement, which had been negotiated to elevate security and defence cooperation between Japan and Australia to a new level," Suga told a joint news conference.

The pact "establishes streamlined arrangements to support the deployment of defence forces more quickly and with less administration", Morrison said.

The two sides also agreed on the need for a framework to allow Japanese military to protect Australian forces if needed, the joint statement said.

Since mid-August, the United States has repeatedly riled China by sending warships to the South China Sea and has blacklisted 24 Chinese entities over their involvement in building and militarising artificial islands there.

China said it was conducting military training in the South China Sea from Tuesday through the end of November.

The legacy of Japan's invasion and occupation of parts of China in World War Two still haunts relations, and the two sides dispute ownership of islands in the East China Sea.