New Zealand Prime Minister Christopher Luxon said he would consider signing up to the alliance, which is aimed at countering Chinese influence in the region.
The Ocean of Peace Alliance was signed on Monday by Australian Prime Minister Anthony Albanese and Fijian counterpart Sitiveni Rabuka, with each country committing to come to the other's aid if they were attacked.
The text of the agreement also opened up the possibility of other Pacific nations joining.
Mr Luxon said he had already spoken to his Australian and Fijian counterparts about the agreement.
"Fiji and Australia this week announced a commitment to become military allies, and New Zealand welcomes this," he said in a statement.
"New Zealand and Australia share a close bond, with a military alliance that continues to go from strength to strength, and we also have a strong and enduring relationship with Fiji.
"We already work with both countries on how we can develop a safer region for all, so engaging with them on this alliance is logical."
New Zealand's only formal alliance is with Australia, while Fiji's signing of the Ocean of Peace Alliance was the first time it had inked a formal agreement.
The alliance adds to Australia's other alliances with the US and Papua New Guinea.
New Zealand Defence Minister Chris Penk said opening up the alliance would be a chance for further cooperation in the Pacific.
"New Zealand values the opportunity to grow Pacific unity and build stronger defence and security partnerships within our region. We are committed to the implementation of deeper defence and security cooperation with Fiji," he said.
A final decision on whether New Zealand commits to joining the alliance will need to be made by the country's cabinet and parliament.
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