In 2019 China publicly announced intentions to increase its military cooperation in the Pacific. That same year the Solomon Islands switched allegiances from Taiwan to China, a move some argue fuelled discontent resulting in recent deadly riots in the capital Honiara.
Mahuta said she was aware of the purported agreement for security cooperation between China and Solomon Islands, which has been shared on social media.
"If genuine, this agreement would be very concerning. Such agreements will always be the right of any sovereign country to enter into.
"However, developments within this purported agreement could destabilise the current institutions and arrangements that have long underpinned the Pacific region's security.
"This would not benefit New Zealand or our Pacific neighbours."
New Zealand and Solomon Islands were "long-standing partners", including in the area of security, and had an active police and NZDF presence there, Mahuta said.
New Zealand sent dozens of soldiers and police officers there in December to assist the local government amid the deadly rioting and unrest, alongside an Australian effort.
Mahuta said New Zealand's High Commissioner in Honiara was raising concerns with the Solomon Islands government and she would be raising concerns directly with China.
"We encourage all partners in the Pacific to be transparent with their actions and intentions, and encourage assistance to be targeted in a manner that enables inclusive and sustainable development and supports regional stability.
"We also strongly support Pacific regional cooperation on security issues as enshrined in the Pacific Islands Forum's Biketawa Declaration.
"We will continue to work closely with all partners to advance the best interests of the Pacific region and New Zealand is focused on supporting long-term resilience outcomes in the Pacific, in line with Pacific priorities."
The ABC reported it verified the document as genuine, but it was a draft and believed to not have been formally signed by both governments.
Australian Trade Minister Dan Tehan told the ABC they were worried the document could undermine the sovereignty of Solomon Islands.
The security pact is likely to also concern the United States, which said in February it planned to open an embassy in the Solomon Islands, citing concerns China wanted to create military relationships in the Pacific islands.
New Zealand's Defence Assessment 2021 warns of risks associated with China's military ambitions in the Pacific, alongside a range of other countries, including the United States.
The assessment warns the "most-threatening" potential development included a military base of dual-use facility being established by "a state that does not share New Zealand's values and security interests".
"Such a development would fundamentally alter the strategic balance of the region," the assessment stated.
"In addition to crowding out access to limited Pacific infrastructure, such a military facility would enable a greater quantity, quality and diversity of military capabilities to operate in and through the region, as well as potentially supporting grey zone and other activities counter to New Zealand's interests."
The assessment also warned of military-backed competition for resources, confrontation and competition among powers.
