The United States is concerned about China's ambitions to extend its military presence in the Pacific after it struck a security pact with the Solomon Islands this year.

"We are doubling down on our investment here in the Pacific," Sherman said. She added that the United States was doing everything possible to engage in the region and promote the rules based international order to ensure everybody can prosper in peace and security.

In the past five days Sherman has met leaders in Samoa, Tonga, Australia and Solomon Islands and attended commemorations which marked the 80th anniversary of the Battle of Guadalcanal. Although Sherman met Solomon Islands prime minister Manasseh Sogavare, he did not attend a dawn service organised by the United States, which local media reported as a "snub."

In New Zealand, Sherman met prime minister Jacinda Ardern and the two discussed coordinating US-New Zealand efforts in the Pacific, including fostering economic prosperity through a free and open Indo-Pacific. The two countries also signed agreements related to space and emergency management co-operation.