Foreign Affairs Minister Nanaia Mahuta says the new Solomon Islands security arrangement with China is unwelcome and unnecessary and should be open to regional scrutiny.

New Zealand and Australia have reacted with frustration to the news Solomon Islands politicians have signed a security agreement with China.

The possibility such a deal could be struck had prompted concerns - shared by the United States, that it could provide for China to establish a military base in the Pacific.

A draft of the deal's text was leaked last month, but the final version that was agreed has not been released, even to the Solomon Island parliament. However it is believed to allow for Chinese forces to help maintain social order in the nation.

China's foreign affairs ministry said Beijing will now cooperate with Honiara on maintaining social order, protecting people's safety, aid, combating natural disasters and helping safeguard national security.

Prime Minister Jacinda Ardern said the arrangement was signed before it could be discussed by Pacific nations, who are all impacted.

China's growing influence in the Indo-Pacific is sure to feature in conversation between Ardern and her Japanese counterpart today. The PM arrived in Tokyo overnight, kicking off the second leg of her international trade mission.

Mahuta said she was saddened the Solomon Islands chose to pursue a security agreement outside the region.

New Zealand has called for the issue to be a top priority for discussion at the next meeting of the 16-nation Pacific Islands Forum, which is scheduled for June. "And I understand a number of other countries have called for that," Mahuta told Morning Report.

"That's the challenge ... bringing this issue into the regional conversation ... around these terms and conditions between China and Solomon Islands."

"Nobody's seen the exact terms and conditions of the agreement, not the whole of the parliament of the Solomons, certainly not the Solomon Island peoples, and not the Pacific Island nations.

The signing of the pact and so-far non-disclosure of its terms is part of a political dispute within the Solomon Islands, but its significance is much wider for the Pacific, Mahuta said.

"I have concerns ... to ensure that this is fully discussed because of the regional implications - that this has not been given priority, certainly by the Solomon Islands. They have given assurances [about the content], we have to take them at their word, respecting their sovereignty.

"However, regional security issues are a matter for a broader forum. We see the Pacific Islands Forum as the best place to bring those issues together so that we can get greater transparency and discuss these."

New Zealand had not yet formally requested the content of the agreement from either China or the Solomon Islands, but: "There has been high level engagement at an officials level, and certainly between ambassadors both in China and in Honiara", Mahuta said.

"The whole of the Pacific want to discuss this issue because no-one's got a lot of visibility on the terms and conditions of the arrangement.

"It's going to be a matter of trying to bring the Solomons into a conversation, rather than the Solomons feeling like they're defending their sovereignty and their being outcast by the rest of the Pacific."

Australian leader of the opposition Penny Wong has accused the Australian government of dropping the ball on their interactions with Solomon Islands before the deal was signed, and allowing what she called the country's biggest foreign affairs failure in 80 years.

Does Mahuta admit to any failure by New Zealand in not succeeding in persuading the Solomon Islands not to go ahead with the deal?

"No," Mahuta said: "New Zealand's upheld it's part of an agreement for the region."

That agreement is The Biketawa Declaration, which was set up by Pacific Islands Forum countries in 2000, and outlines how the parties to it will respond to a regional crisis.

It has previously been invoked to assist Solomon Islands with unrest inside the country, with New Zealand among nations who sent assistance in response to riots and buildings burned in Honiara late last year, as well as an operation that wound up in 2017. It was also invoked in response to the Tonga eruption earlier this year.

"We are the closest neighbours, we can respond," Mahuta said.

Both China and Solomon Islands have dismissed fears a Chinese military base could be established in the Solomon Islands. But if this did happen, or if Chinese military personnel had a presence in the Solomon Islands, would that constitute a "diplomatic red line" for New Zealand?

"Both China and the Solomons have been at pains on this recent signing to say that that is not the case," Mahuta said.

"New Zealand by extension has said well, then we need to discuss these issues as a part of the Pacific Islands Forum, so all Pacific nations have the ability to hold those statements to account, but also to investigate the terms and conditions of the arrangement."

Questions need to be asked about why it was signed - National

National said the government must ask itself why Solomon Islands looked past its traditional allies to China for a security deal.

The party's foreign affairs spokesperson Gerry Brownlee said the development was a diplomatic failing.

New Zealand should now consider extending its existing peacekeeping deployment in Solomon Islands, given growing volatility in the region, he said.

'Mixed' reactions to the deal in Solomon Islands

Honiara-based freelance journalist Gina Kekea told Morning Report there had been dissatisfaction in Solomon Islands around the deal, particularly the lack of transparency about what has been signed.

"Not much" is known about what's in it: "The framework of the agreement was based on the National Security Strategy which the government completed in 2020... and the leaked document that was shared by social media recently.

"It's something which is a worry... the process has to be as transparent as possible, so everyone will understand."

Sogavare has indicated the Solomon Islands will have to follow certain processes as a result of the agreement, and the country's permanent secretary of foreign affairs has told a press conference the document will be made available, Kekea said.

He had defended the deal as being in the best interests of the Solomon Islands and its people for keeping peace, said they had entered into the deal "eyes wide open", and that as a sovereign nation the country can make agreements with any country they see fit.