The NZ Herald seems to hint that the activity may be a warning and a new alliance to "contain" China (which I doubt our readers need reminding has not militarily challenged anyone in a while).
China and Russia did hold some military exercises themselves with some smaller nations included and India invited and onlooking a little while ago.
Or maybe this latest exercise really is about sealane security.
Excerpt New Zealand Herald "Five-power naval exercise gives China the jitters ":
The manoeuvres, which began yesterday, are an extension of long-running bilateral naval exercises between India and the US, known as the Malabar series. They have been expanded for the first time to include Australia, Japan and Singapore. The US will contribute 13 warships, India seven and Australia will be represented by a frigate and a tanker, Japan by two destroyers and Singapore by a frigate.
The operational zone for the training stretches from the Indian mainland to India's Andaman and Nicobar Islands, guarding the western approaches to the Malacca and Singapore straits, one of the world's busiest waterways.
Some 60 per cent of China's foreign trade and 75 per cent of its oil imports pass through these straits. The formation of a quadrilateral dialogue between the US, Japan, Australia and India is being pushed by Tokyo and Washington on the basis that the four share common values of freedom and democracy, and should co-operate to advance other shared interests.
Australia and Japan are allies of the US. Last March, Canberra and Tokyo signed a Joint Declaration on Security Co-operation. Their foreign ministers hold a regular trilateral strategic dialogue with the US to co-ordinate approaches to regional security and stability. When the US and Japanese foreign and defence ministers met in Washington in early May, they made a direct reference to the importance of engaging India.
The statement said it was their common strategic objective to continue to build on partnerships with India to advance areas of common interests and increase co-operation, recognising that India's continued growth is inextricably tied to the prosperity, freedom, and security of the region.
For Japan, India is a key part of the Arc of Prosperity and Freedom that the Abe government is trying to build around the outer rim of the Eurasian continent skirting the borders of China and Russia. The Arc partnership appears to exclude Beijing and Moscow.
When senior officials of the US, Japan, India and Australia arranged an inaugural meeting on the sidelines of a meeting in Manila in May of the Asean Regional Forum to discuss how to take the four-power relationship forward, China pointedly sent diplomatic notes to each of them requesting an explanation. Since then, Beijing has indicated that if the Quad is formed, it will be divisive, destabilising and risk plunging Asia into another Cold War.
Please read rest of this short article at link above. It is so well crafted that I was tempted to excerpt most of it here. Not long, but full of information.