Secret planning has begun for a new port facility just outside Darwin which could eventually help US Marines operate more readily in the Indo-Pacific.

Key points: Australia is considering a new commercial port that may be used by US Marines

Australia is considering a new commercial port that may be used by US Marines Senior defence and government figures say plans for the new facility may cause angst in Beijing

Senior defence and government figures say plans for the new facility may cause angst in Beijing A Chinese company has leased the Darwin Port for 99 years

Precise details remain tightly guarded but senior defence and federal government figures concede the proposal may risk angering China even though it's a commercial port, not a new military base.

Multiple officials, speaking on the condition of anonymity, have confirmed to the ABC the multi-use development would be in the Glyde Point area, roughly 40 kilometres north-east of Darwin's existing port.

In the past, the location has been earmarked by the Northern Territory Government as a possible future industrial port site given its relatively deep waters, but funding arrangements for the yet-to-be announced project remain unclear.

Darwin port, which was controversially leased to a Chinese company in 2015, has existing defence facilities such as a multi-user barge ramp, but the new proposed facility would have the additional advantages of being less busy and less visible.

If approved, the new port could eventually be able to accommodate large amphibious warships such as Australia's Landing Helicopter Docks, and American vessels such as the USS Wasp, which recently arrived in Sydney.

The new facility is planned at Glyde Point, about 40 kilometres from Darwin. ( ABC News: Mike Donnelly )

Strategic experts believe a new deep-water port would be ideally suited for the more than 2,000 US Marines and their equipment during regular rotations through the Top End.

"The Americans are clearly not withdrawing from the Indo-Pacific, whether it's because of their strategic competition with China or more generally," said Rory Medcalf from the Australian National University.

"It's clear the Americans intend to stay in the region to reinforce their presence, to reinforce the alliance, and so a facility like this would be quite a logical development I think."

The ABC approached the Defence Department and the US Embassy in Canberra for comment, but both are yet to respond to detailed questions on timing and costs.

In a statement, the department simply insisted "Defence has no plans for the development of a new naval facility in the Northern Territory", while the US embassy declined to comment.

The Federal Government referred all questions about future port development to the Territory Government, but a spokesman for NT Chief Minister Michael Gunner said he was not aware of any proposal.

It's understood a formal announcement on the new maritime facility could be made as early as next month when the "Talisman Sabre" war games with the US begin in the Northern Territory and Queensland.

One senior Commonwealth source said any public unveiling had been deliberately delayed until well after the recent Indonesian presidential election race, but would still be likely to cause angst in Beijing.

"I'd be surprised if the Chinese don't already know about it, but they can't complain because they're building similar ports in this region," the senior figure told the ABC.

Another source familiar with early discussions on the proposal claimed the United States had examined various options in the region to berth large amphibious assault ships, including Singapore, but had concluded Northern Australia was the best strategic location.

Recent hints point to American ambitions in Top End

An imminent announcement of a new maritime facility in the Northern Territory would not come as a complete surprise for Darwin locals and close strategic observers of the recent military build up in the Indo-Pacific.

Recently, a $40 million road was constructed to Gunn Point, near Glyde Point, a project which was completed quickly and was said to be for improving access to fishing areas.

Cattle being loaded at the Darwin Port, which was leased to Chinese company Landbridge for 99 years. ( Carl Curtain )

In 2015, the year Chinese company Landbridge began a 99-year-lease of Darwin Port, the US's then-chief of navy operations, Admiral Jonathan Greenert, revealed the Pentagon was considering having a permanent naval base in Australia.

Just last month the Pentagon's latest Indo-Pacific Strategy Report stated that the United States was seeking to "evolve our posture and balance key capabilities across South Asia, Southeast Asia, and Oceania to have a more dynamic and distributed presence and access locations across the region."