A United States Defence build-up in the Northern Territory is being welcomed by local businesses and watched closely by wary northern neighbours, as some of the world's deadliest fighter aircraft arrive.

Defence analysts say the increasing presence of US Marines in the Top End is a clear sign the US is bolstering its military presence in the region, as a squadron of its sophisticated F-22 Raptors touched down near Katherine this weekend for three weeks of exercises with the Australian military.

That will soon be followed by the next rotation of US Marines and a large contingent of aircraft.

The Defence Department said it constituted the largest and longest rotation of fifth-generation aircraft to Australia to date.

Dr John Blaxland from the Australian National University's Strategic and Defence Studies Centre said it was clear "the US has a much more robust presence in Australia."

Dr Blaxland said while there was "a fair degree of assurance" the current arrangement with US troops in Darwin would remain, "in terms of the US posture in South East Asia and the region more broadly there's enormous uncertainty".

"Does this mean the US administration will take a more confrontational approach towards China, say, in the South China Sea?

"If that's the case that has potential to have significant consequences in the neighbourhood; there'll be considerable pressure on Australia to participate and to facilitate that engagement."

Chief Minister Michael Gunner said he would work hard to help local businesses seize the opportunity of Defence contracts over the coming years. "I'll be in Canberra, knocking on doors, I will be opening them, and sometimes as the Chief Minister I can open doors the private sector can't," Mr Gunner said.