New Zealanders who have worked in Australia and had to leave their compulsory retirement savings behind when they came home will be able to repatriate the funds under an agreement announced today.

Australia's Tax Office estimates about A$13 billion ($16.6 billion) is held in "lost" accounts within the superannuation system.

The agreement, which works both ways, was reached at a meeting in Brisbane between Finance Minister Bill English and Australian Treasurer Wayne Swan.

It has been assumed that most of the money held in the "lost" accounts belongs to New Zealanders, but Mr English told NZPA that could not be confirmed.

"They genuinely don't know," he said.

"We can't assume anything, but a proportion of it will belong to Kiwis."

Mr English said there were many New Zealanders who had worked in Australia and had kept track of their retirement savings.

"Those are Kiwis who haven't `lost' their accounts, and now they'll be able to bring the money back as well."

Portability will operate between the official Australian superannuation fund and New Zealand's KiwiSaver scheme.

Mr English said although Australians who had worked in New Zealand could send their savings home, New Zealand was likely to benefit the most.

"There will be more New Zealanders with more money in Australian accounts than Australians with money in KiwiSaver accounts, if only because KiwiSaver is so new," he said.

Participation in the portability scheme will be voluntary and legislation will have to be passed before it can come into effect.

Mr English said he expected the legislation would be passed within 12 months.

The ministers said in a joint statement after their annual bilateral meeting that they also made "significant progress" towards a single economic market during their annual bilateral meeting.

The new Australia-New Zealand tax treaty was finalised and they discussed the work being done to harmonise regulations.