(CNN) Australia is spending billions on unmanned American spy drones that will be able to fly higher and further than its manned aircraft, to beef up its surveillance operations in areas that include the disputed South China Sea.

On Tuesday Australian Prime Minister Malcolm Turnbull said his government was investing $6 billion to acquire six MQ-4C Tritons, remotely piloted aircraft, from US defense contractor Northrop Grumman , "through a cooperative program with the United States Navy."

The Tritons would complement the current surveillance aircraft Australia already uses to survey its maritime borders, conduct search and rescue, and carry out Freedom of Navigation exercises in the contested South China Sea.

Defense Industry Minister Christopher Pyne told the Australian Broadcasting Corporation that the drones, which can travel up to 25,000 miles, will also be used to track foreign ships, smugglers and pirates.

The aircraft, which have a de-icing capability, will fly as far north as the Indian Ocean, and as far south as Antarctica, where the Australian military monitors activity over the country's Exclusive Economic Zone , a marine area of around 4 million square miles.

"It is very important for us to know who is operating in our area and therefore be able to respond if necessary to any threats," Pyne told ABC News.

"Australia insists on its right to be able to travel through the South China Sea in international waters as we have always done, whether that is with surface ships or with aircraft."

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Whatever intelligence the Australian Navy is able to glean from its surveillance operations will be shared with the other nations that are members of the "Five Eyes" -- the United States, New Zealand, Canada and the UK.

The acquisition of the drones was first announced by former Prime Minister Tony Abbott in 2014

"I think there is a view that this is a long time coming, previous prime ministers have been talking about these things, now it's real, not just an idea," said Michael Shoebridge, director of defense and strategy at the Australian Strategic Policy Institute.

He believes the announcement was prompted by the news that Canberra was spending $150 million of that money on a joint program with the US Navy to develop and sustain the aircraft at the Royal Australian Air Force base in Edinburgh, north of Adelaide, the capital city of South Australia state.

"I don't think this will be news for the Chinese because it's been a public thing that the Australian government has been investing in it," Shoebridge told CNN. "It'll just complement the Freedom of Navigation and overflight activities that the Australian Navy and Air Force are doing all the time, but it is making the point that it is having more Australian presence up there."

China has repeatedly challenged Australian warships , most recently in April when three Australian navy vessels were on their way to Vietnam for a goodwill visit.

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China claims a great swathe of the South China Sea as its own territory, a claim that overlaps with Vietnamese and Filipino and other regional interests. The waters are some of the most hotly contested in the world.

Beijing held its own drills in the disputed territory in April, including a huge military parade overseen by Chinese President Xi Jinping.

To reinforce its claims in the region, China has constructed and militarized a series of artificial islands across the South China Sea, building airfields and radar stations. Last month US warships sailed past some of the disputed islands, drawing a rebuke from Beijing

A statement from ministry spokesman Lu Kang called on the US to "immediately stop such provocative actions that encroach upon China's sovereignty and threaten China's security."

The first of the new spy drones are not expected to come into operation until 2023, Turnbull announced, adding that all six would be delivered and in operation by late 2025.

Shoebridge said that the drones could be operated from South Australia even as they are launched from Darwin, 1,900 miles north of the air force base. Currently Darwin is also home to 1,500 American Marines

The Marines are on their seventh rotation where they train alongside Australian forces as part of a military alliance between the two countries that began with World War I.

Part of that alliance now serves to check China's expanding influence in the Asia-Pacific, of which those freedom of navigation exercises are key.

Australian defense minister Marise Payne announced on Monday that as part of its "long-standing commitment to regional security," facilities at a Malaysian air force base used by the Australian military would get a $16 million upgrade.

You can't have freedom of navigation and overflight if you don't exercise it," said Shoebridge of the Australian Strategic Policy Institute.

"It's empty words unless you have physical presence," he said.