The United States military is preparing to spend more than a quarter of a billion dollars on naval construction in the Northern Territory, in a move that could raise tensions with China.

Key points: A draft US bill allocates $US211,500,000 for Navy military construction in Darwin

A draft US bill allocates $US211,500,000 for Navy military construction in Darwin Australia's Defence Department says the US bill has not been approved

Australia's Defence Department says the US bill has not been approved The legislation also proposes several other US projects in the NT

A recent draft US Congressional bill uncovered by the ABC reveals a total of $US211.5 million ($305.9 million) has been allocated for new "Navy Military Construction" in Darwin, but few other details are available.

According to the Senate's annual defence legislation, tabled in June, the "Secretary of the Navy may acquire real property and carry out military construction projects for the installations or locations outside the United States".

Just last month the ABC revealed that secret planning had begun for a new commercial port facility just outside Darwin which could eventually help US Marines operate more readily in the Indo-Pacific.

Following the report, Australia's Defence Department insisted it had "no plans for the development of a new naval facility in the Northern Territory", while Northern Territory Chief Minister Michael Gunner denied any knowledge of such a proposal.

In 2015, Washington expressed disappointment after Chinese company Landbridge was given a 99-year-lease of Darwin's existing port, but Federal Government sources privately concede any new maritime facility which could be used by American personnel also risks angering Beijing.

A new facility is being planned at Glyde Point which could help US Marines operate more readily in the Indo-Pacific. ( ABC News: Mike Donnelly )

Last week Australia and the United States both expressed concerns at an apparent secret deal allowing China exclusive rights to a Cambodian naval installation in the Gulf of Thailand.

Now, in response to fresh questions from the ABC, the Defence Department says it is still too early to comment on what the US military may have planned in the Northern Territory.

"The referenced document is the Senate version of the National Defense Authorization Act, which authorises (but does not appropriate) Defence initiatives," the Department said in a statement.

"It is still progressing through the US Congress and must be reconciled with the House version before it is finalised. It is not yet approved.

"We expect the US Department of Defense will provide details of the funding in accordance with its processes and timelines following consideration and approval within the United States Government."

The legislation says the US Navy may acquire property and carry out construction outside the US. ( Supplied: Staff Sergeant Jordan Gilbert )

However, the Defence Department insists the proposed funding, which is associated with United States Force Posture Initiatives (USFPI) projects, are "negotiated and agreed to by both Australian and US Governments".

Last week, Defence Minister Linda Reynolds announced that the Marine Rotational Force in Darwin had "reached full strength", with 2,500 US Marines now deployed in the Top End.

The draft US legislation also outlines several other proposed spending projects in the Northern Territory including $US50 million for a "new airport parking apron for the Navy", and $US70.6 million for the Air Force at Tindall.

The ABC has approached the US Embassy in Canberra for comment.

Loading...