The blocks have been acquired in a move to shore up future land supply as discussions continue about the possibility of shifting the ACT's borders to include the NSW portion of Ginninderry.

The territory government's Suburban Land Agency paid more than $8 million for one of the blocks on Parkwood Road. A call-option deed has been placed on the other block and the selling price has not been disclosed.

But the ACT government has plans to purchase an additional two blocks to expand the Ginninderry development.

Legislation was changed last month to allow the ACT government's Suburban Land Agency to purchase land in NSW.

Housing and Suburban Development Minister Yvette Berry at the time refused to reveal what land the government, if any, had planned to buy citing commercial reasons.

The Suburban Land Agency has publicly announced the land acquisition after The Canberra Times obtained documents under freedom-of-information laws outlining the government's plans to buy four blocks in NSW.

The blocks in NSW have been slated to be part of the Ginninderry development since the initial stages of planning.

However, the owners of the neighbouring blocks only indicated a willingness to sell last year after the blocks were rezoned to allow residential development.

Freedom-of-information documents outlined that Riverview commenced sales negotiations with the owners in 2013 and 2017, but they were unwilling.

"On both occasions, the landowners were not ready to sell given the potential uplift in the value of the land once rezoned," a document said.

"Finalisation of the rezoning has prompted the sale negotiation process to recommence in 2020. Three owners have now indicated a willingness to entertain negotiations."

The owners of the four blocks did co-operate with the rezoning process but refused to fund costs associated with it. Instead this was bankrolled by Riverview but the group will seek to recoup these costs from the owners, documents showed.

"The benefits to the [joint venture] of the inclusion of the NSW neighbours lands were considered to outweigh the costs to Riverview," documents said.

"A successful rezoning would result in a benefit to the NSW owners as their land values would be uplifted."

The ACT government entered into the joint venture to develop Ginninderry with Riverview in 2016. Riverview is a subsidiary of the Corkhill Brothers group.

Under the joint venture agreement, Riverview retained ownership of land it held in NSW but its land in the ACT was sold to the territory government for $4.5 million.

There is expected to be about 30,000 residents and 11,500 homes across four suburbs. The development would span about 1600 hectares across the ACT and NSW with homes to be built on about 800 hectares.

The NSW land will not be developed for about another decade, with the land bought by the ACT government to remain farming land until it is developed.

The two blocks the ACT government has agreed to buy will add about 160 hectares and 480 properties to the development.

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Suburban Land Agency chief executive John Dietz said the acquisition of the NSW blocks would provide more options for Canberra's future.

"Adding to the future land release program in west Belconnen is an excellent outcome for Ginninderry," he said.

"This will provide opportunity for the growing Canberra region in terms of choice, affordability and location."

Earlier this year, the ACT government paid more than $50,000 to real estate agents to undertake valuations of the blocks.

The reason given for the valuations at the time was that the Suburban Land Agency was seeking to understand the value of the land due to the proximity to the Ginninderry development. There was no mention of the forthcoming acquisition.

The ACT government is still fighting for the borders to be changed so that the NSW land in Ginninderry is incorporated into the territory.

Ms Berry told question time last month that discussions were continuing with the NSW government, the Commonwealth and Yass Valley Council about moving the border.

"The government's position has been well broadcast; our preference is for the borders to be moved, so that those parts of NSW become part of the ACT. That would make things a lot easier for everybody to navigate," she said.

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