Salt Funds Management managing director Paul Harrison said increasing the shareholding was a good strategic move for Air New Zealand and protected its revenue gains from the transtasman alliance.
The partnership connects Air New Zealand's 26 domestic destinations in this country with Virgin Australia's more than 35 domestic Australian destinations and strengthens the Kiwi carrier's position against Qantas and Emirates in the highly competitive transtasman market.
"Air New Zealand has seen Etihad start to increase its stake [in Virgin Australia] a little bit, so they'll be trying to make sure they don't lose influence," Harrison said.
Forsyth Barr head of private wealth research Rob Mercer said Virgin Australia was a key part of the New Zealand carrier's Australasian strategy and the plan to increase the stake showed the investment was seen as a long-term one.
"To be strong in the Pacific Rim does require Air New Zealand to have a good network into Australia."
Analysts were not worried by the financial position of Virgin Australia, which posted a net loss of A$98.1 million for its last financial year.
Air New Zealand chief executive Christopher Luxon said the opportunity to increase the shareholding and the recent extension of the transtasman alliance meant the airline could work "confidently" with Virgin Australia to provide a competitive Australasian and international network.
Shares in Air New Zealand closed up 0.5c yesterday at $1.50.