The United States Defence Secretary Lloyd Austin, on Thursday announced the deployment of a US Coastguard ship to Papua New Guinea, as Washington seeks to boost its military footprint in the region amid fierce competition for influence with China.

"A US Coastguard cutter will be here in August," Austin said as he became the first Pentagon boss to visit Papua New Guinea.

Austin stressed that the coastguard deployment would help Papua New Guinea stop the plundering of its thinly protected maritime resources, stopping activities like illegal fishing and trafficking.

The move capitalises on a recently signed defence pact between the two countries that offer the United States greater military access to a strategically important part of the South Pacific.

US is keen to show that regional partners can benefit from increased US security cooperation and to allay local fears that Papua New Guinea is being dragged into a US-China battle for influence in the region.

Perched between Taiwan and US ally Australia, Papua New Guinea is the largest and most populous state in Melanesia, an area that was pivotal in deciding the outcome of World War II in the Pacific.

According to a landmark US-Papua, New Guinea security pact signed earlier this year, the United States will be able to develop and operate out of facilities across the country.

With Papua New Guinea's agreement, the US military can station troops and vessels at six key ports and airports, including Lombrum Naval Base on Manus Island and facilities in the capital Port Moresby.

Washington would have "unimpeded access" to the sites to "pre-position equipment, supplies and materiel" and have "exclusive use" of some zones where development and "construction activities" could be carried out, according to the text.

Lombrum has in the past been used as a garrison for British, German, Japanese, Australian and US troops.

During World War II, it was one of the largest US bases in the Pacific, with 200 ships at anchor, including six battleships and 20 aircraft carriers that were used to retake the Philippines from Japan.

But Austin tried to allay concerns that the pact would erode the South Pacific nation's fiercely guarded independence.

Papua New Guinea only escaped decades of direct rule from Britain and Australia in 1975.

"I just want to be clear that we're not seeking permanent basing in PNG," Austin told his hosts. "This is an opportunity to expand upon a long-standing relationship."