Chinese vessel believed to be spy ship docks next to HMAS Adelaide in Fiji

It may not have looked like much of a match — or a showdown for that matter — but when Australia's largest warship HMAS Adelaide arrived at the Fijian port of Suva on Saturday, it had an interesting neighbour.

A Chinese ship fitted with communications equipment docked alongside the new Canberra-class landing helicopter dock.

The Royal Australian Navy suspects the Chinese vessel is a spy ship, which deliberately arrived at the same time to carry out surveillance on the Australians.

HMAS Adelaide and other Australian warships visiting Fiji will "take the appropriate security precautions", but the surveillance craft is "just another ship", Captain Jim Hutton, Commander of the Navy's Joint Task Group 661, said.

Deputy Chief of Navy Rear Admiral Mark Hammond also played down concerns about the presence of the Chinese vessel.

"That's a space surveillance ship, it's a scientific ship," he told reporters on board HMAS Adelaide.

ABC News understands the primary purpose of the Chinese ship is to track satellite launches from out on the ocean, but it does have the capability to also collect intelligence on other naval vessels.

Australia's High Commissioner to Fiji John Feakes also revealed the skipper of the Chinese vessel had even been invited to an on-board reception, although it is not clear whether the offer was accepted.

Australia's Navy, like every navy around the world, is well-versed in these sorts of nautical games.

"If you're in the Navy you presume that anytime that a fishing vessel or even merchant fleets of nations like China are around that they may have a dual purpose," ANU academic and retired Australian Naval Commodore Richard Menhinick said.

China's looking for South Pacific foothold

Chinese presence — both commercial and military — is common in the South Pacific.

Beijing sees economic opportunity in the region and economic imperatives commonly herald other strategic interests.

Agriculture and aquaculture projects in Vanuatu, Fiji, Tonga and other Pacific nations have been given significant help by the Chinese over the years, as have roads, ports and other infrastructure.

When you have more than 1.3 billion people back home to feed, finding secure food supplies are critical.

As China grows, Mr Menhinick said it was not surprising that the nation's presence in the Pacific was also increasing.

"China's a rising power… economic power's always led and the military's followed, and the Chinese economic interest in the south-west Pacific has increased substantially over the last fifteen year," he said.

But Australia and its strategic partners are anxious China does not use its presence to jeopardise regional structures — political, economic and diplomatic.

Now a visiting US General has given the strongest public indication yet that his nation would like Australia to join in naval and air patrols to challenge Beijing's claims in the South China Sea.

Asked whether joint American-Australian patrols would be welcomed by America, the commander of US Marines in the Pacific, Lieutenant General David Berger gave an enthusiastic response.

"Obviously that's Australia's decision, would we welcome that? Absolutely yes," Lt Gen Berger said.