China on Tuesday announced it had signed the controversial agreement that would allow Chinese police to protect infrastructure and social order in the Pacific nation, despite strong overtures from Australia, New Zealand and the United States.

Canberra is concerned the deal could ease the way for a Chinese military presence less than 2000 kilometres from Australia's shores.

The US was so concerned about the ramifications of the deal it had dispatched its top diplomat for the region, Kurt Campbell, to lead a delegation to the Solomon Islands, Fiji and Papua New Guinea.

But before Mr Campbell touched down in the region, China's foreign ministry spokesman Wang Wenbin said the deal had been signed.

"Despite all of his tough talk, on Scott Morrison's watch our region has become less secure," opposition foreign affairs spokeswoman Penny Wong wrote on Twitter.

Senator Wong accused the prime minister of failing to send Foreign Minister Marise Payne to the Solomon Islands to address Australia's concerns, despite the government being "warned of this security pact in August".

Minister for International Development and the Pacific Zed Seselja last week travelled to Honiara to ask Solomon Islands Prime Minister Manasseh Sogavare not to sign the agreement.

Together with the foreign minister, Senator Seselja issued a statement on Tuesday evening outlining Australia's "deep disappointment" with the signing of the co-operation agreement.

"We respect Solomon Islands' right to make sovereign decisions about its national security," the senators wrote.

"Our consistently stated view, including from the perspective of Australia's national interests, remains that the Pacific family is best placed to meet the security needs of the region."

The senators outlined a lack of transparency in the development of the agreement and said the government continues to seek clarity on its terms and the consequences for the region.

"We welcome recent statements from Prime Minister (Manasseh) Sogavare that Australia is Solomon Islands' security partner of choice, and his commitment that Solomon Islands will never be used for military bases or other military institutions of foreign powers," the statement said.

"Australia is consulting the Pacific family in the spirit of regional openness and transparency in a manner consistent with our regional security frameworks.

"We will continue to strongly encourage the Solomon Islands to engage in regional dialogue and to work with the Pacific family first, including prior to seeking security assistance from China under this arrangement."

Australian Associated Press