The United States and Japan said Thursday Tokyo would pay a third of the cost of Washington pulling thousands of Marines out of Japan as it reduces its heavy military presence on Okinawa.

US Secretary of State John Kerry, Secretary of Defense Chuck Hagel, Japan’s Foreign Minister Fumio Kishida and Defense Minister Itsunori Onodera signed the protocol amending the 2009 Guam International Agreement, as part of a meeting on the two countries’ alliance.

Changes include “clarifying that Japan will contribute up to $3.1 billion in Fiscal Year 2012 US dollars in direct cash contributions to develop facilities and infrastructure in Guam and the Commonwealth of the Northern Mariana Islands”, the state department said.

It accounts for 36 percent of the projected $8.6 billion cost of the relocation.

In a 2012 agreement, the United States said it would pull 9,000 Marines out of Okinawa — 4,000 of whom would go to Guam and 5,000 to Hawaii and on rotations to Australia — as it seeks to ease a long-running standoff over the future of its huge military presence in one of its top Asian allies.

Defence was asked about any sensitivities over Darwin's China port deal, the NT Government says.

Defence was consulted prior to the deal being sealed, after a NT parliamentary committee noted the strategic position of the port and warned no foreign investment should occur that threatened the country's security interests.

While a Federal Government spokesperson said Defence secured a 15-year access agreement to the port in anticipation of the lease occurring - they also said it was spending millions of dollars on an alternative barge facility in Darwin.

The Maritime Union of Australia (MUA), which is against the deal, has labelled the lease a strategic worry for the Top End, which plays host to a large Australian Defence presence and yearly rotations of USA Marines.

The USA Chief of naval operations, Admiral Greenert, when he was in Australia last year clearly identified port infrastructure needs in Darwin as a critical element to the growth of 'cooperation' in Darwin.

Parliament has approved an $18 million project to build a barge facility at a site adjacent to the Darwin port that will be capable of loading and unloading giant amphibious naval ships at short notice.

As a parade of senior Australian and United States commanders and their public affairs teams attempted to stay on message about the “humanitarian” aspects of the biggest military exercise ever in Australia — the shadow of China was cast over every facet of the intensive war gaming.

During a lightning visit to the exercise area on Sunday, Prime Minister Tony Abbott insisted that China appreciated that Australia was an ally of the United States.

Mr Abbott further confused things when he declined to rule out the possible future permanent basing of USA forces in Northern Australia.

The Marine Corps training rotation is scheduled to grow from 1100 now to 2200 in the next few years, but Mr Abbott left the door open for even greater access for USA forces to the deserted and wide-open training ranges of Northern Australia.

When asked specifically if there would be USA forces based in the north the prime minister was noncommittal.

“Let’s see what the future holds. I am not saying there will be more … but they shouldn’t shock or surprise anyone.”

Ask any of the thousands of USA Marines participating in Talisman Sabre — particularly those based on the tiny island of Okinawa in Japan — and they will tell you that the NT and Rockhampton are war games nirvana.

A man is cut out of a ute after it crashes with a USA Marines vehicle in Katherine in the NT.

Police said the crash happened at 1:45pm at the junction of the Victoria and Stuart highways.

The 34-year-old man was trapped in the ute for about 45 minutes while emergency services diverted traffic and attempted to free him from the wreckage.

Police told the ABC the man has been taken to Katherine Hospital with non-life-threatening injuries.

The six-wheel off-road truck is called a Medium Tactical Vehicle Replacement - a vehicle used by the USA Marines to haul equipment and troops.

AUSTRALIAN and American environmental specialists were cleaning up a suspected fuel spill at a popular Darwin beach on Wednesday.

The ADF and Marines were notified of a marine fuel spill on Casuarina Beach, off Lee Point on Tuesday.

Results of sand quality testing revealed an area about 20m long and 10m wide that may have been contaminated in a spill which occurred during an amphibious offload as a part of Exercise Talisman Sabre — Australia’s largest combined military exercise, which runs through until July 21.

A spokesman said the ADF had “notified all appropriate government agencies”.

“The ADF’s environmental team took immediate steps to cordon the area and began to assess the extent of the incident,” he said.

It’s not known what caused the spill.

"It’s not known what caused the spill" - you don't think it might have been that big old Landing Craft that kept coming up onto the sand?