NPR:
Details of the agreement have not been made public, but a draft was leaked last month, and it set off alarm bells in Australia and the United States. If the final version is unchanged, China will be able to deploy police or soldiers to the Solomon Islands for training and to help maintain order. It could also make naval ship visits.
Despite denials from Beijing and Honiara, there’s concern that China could eventually even open a naval base there. Australian Prime Minister Scott Morrison said that would cross a red line, and senior U.S. officials visited the Solomon Islands to explain Washington’s stance. Assistant Secretary of State Daniel Kritenbrink was one of them.
See also: U.S. Turns The Screws On Solomon Islands To Counter China