High-tech Chinese ships are mapping waters close to Papua New Guinea as the United States and Australia begin upgrading a naval base on Manus Island.
The deep-water Chinese scientific surveys are part of Beijing's unprecedented oceanographic research of the Western Pacific.
Military analysis of GPS satellite data reveals two Chinese research vessels entered PNG's Exclusive Economic Zone north of Manus Island, just weeks after US Vice President Mike Pence announced a joint redevelopment of the ageing Lombrum naval base.
The ships involved, the Ke Xue and Hai Ce 3301, are part of a two-dozen strong Chinese "Distant-Ocean Research fleet" which has conducted expansive maritime surveys around the Philippines, Palau, Guam and Japan over the past two years.
Senior Australian and American military officials acknowledge the oceanographic surveys are entirely lawful, but believe the civilian ships are also gathering invaluable data for future defence operations.