US Marines are set to arrive in Australia's tropical north next month as Washington increases its military presence as part of a renewed emphasis on the Asia-Pacific, reports said Tuesday.

State radio said about 250 Marines were set to deploy to Darwin from early April as part of a process that will see about 2,500 in Australia by about 2016, according to a plan announced by President Barack Obama last year.

"This first year, of course, we start pretty small," the commander of Australia's First Brigade, Brigadier General Gus McLachlan told the Australian Broadcasting Corporation.

"We have got about 250 arriving in early April. This first year is almost just a foot in the door, proof of concept, and obviously it will build up in a pretty measured pace in the next few years."

Obama announced plans to increase the number of troops, aircraft and ships that will come to the Northern Territory during his first visit as president to Australia in November.

The move rankled China and caused concern for some Asian neighbours who saw it as a statement by Washington that it intends to stand up for its interests in the region amid concern about Beijing's growing assertiveness.

But there will be no US bases on Australian soil, with the Marines accommodated in existing Australian bases as they conduct exercises and training on a six-month rotational basis.

During his visit to Australia, the self-declared "Pacific President" told reporters at a press conference with Australian Prime Minister Julia Gillard that when it came to the region: "We are here to stay."

"This is a region of huge strategic importance to us," Obama said.

"And we are going to make sure that we are able to fulfil our leadership goal in the Asia-Pacific region."

Australia and the United States also agreed to enhance cooperation between their air forces, resulting in increased rotations of US planes through northern Australia, which is closer to Asia than it is to Sydney and Melbourne.

The United States currently has only a limited deployment in longstanding ally Australia, including the Pine Gap Joint Defence Facility spy station near Alice Springs.