Australia's involvement in the Pacific region should not be prompted by concerns over China, says Labor.

The Morrison government has announced a $5 million deal between Australia and Papua New Guinea to develop a joint naval base on Manus Island, but has remained tight-lipped on whether the project is to prevent China from building a port.

Opposition defence spokesman Richard Marles refused to speculate on the government's motivations, but said there was no doubt Australia's strategy would change if China developed a base in the Pacific.

However, Mr Marles says the genuine benefit of the Pacific nations should be the focus.

"If our engagement in the Pacific has as its goal the strategic denial of China ... we won't succeed, we will not get policies right," he told Sky News on Sunday.

"It will be sniffed out with a high degree of cynicism by the countries of the Pacific themselves."

Australia should do more to not only increase Papua New Guinea's defence capabilities but our overall military cooperation in the region, he added.

"This can be done well, it can be done badly. Diplomacy really matters here."

Papua New Guinea's Lombrum Naval Base on Manus Island will support four new Guardian-class patrol boats, Defence Minister Christopher Pyne said on Saturday.

"Australia is proud to support the PNG Defence Force in strengthening their maritime security capability, and remains committed to our longstanding partnership," he said in a statement.