The China warship just 150 nautical miles off Sydney is one of the ...

Among the Chinese naval vessels detected only 150 nautical miles (276km) off the Sydney coast is one of the world's most powerful warships.

The Australian Defence Force confirmed today it had been monitoring the flotilla since it was first detected in international waters off north-east Queensland last week.

The People's Liberation Army-Navy ships include the Renhai-class guided missile cruiser Zunyi, one of the world's most advanced warships.

"It is one of the largest in the world, and a really powerful and modern warship," said defence analyst Sam Roggeveen, of the Lowy Institute think tank.

Weighing in at about 12,000 tonnes, they are larger than comparable vessels built for the US Navy.

They are also equipped with 112 missile tubes, twice the firepower of the Royal Australian Navy's most lethal warship, the air warfare destroyer.

"The Renhai class is a major statement of ambition by the PLA navy. It is a formidable design," said Roggeveen.

Despite the show of force by China, there are logistical challenges involved in deploying warships so close to the Australian coast, says Roggeveen.

"It's very difficult to deploy ships routinely, consistently over such vast distances.

"The Chinese still can't do that, they can do it every once in a while, but not at a high tempo."

But this scenario could change if China gained a naval base further south in the Pacific Ocean.

That would make it easier for the PLA Navy to deploy warships along the Australian coastline, with the ADF having to respond with increased surveillance.

"It means that we chew a huge amount of resources just monitoring that activity ... If there were a (Chinese) base or more bases in our neighbourhood, it would become routine."

"The entire Defence force would have to spend a lot more time and a lot more money just keeping an eye on it."