WELLINGTON, Aug. 1 -- Chinese food giant Shanghai Pengxin Group on Friday confirmed it was seeking to buy another major New Zealand dairy holding, stepping into a general election campaign row over foreign purchases of New Zealand's productive farmland.

The sale, which is subject to approval by New Zealand's Overseas Investment Office (OIO) and Chinese authorities, was revealed by the leader of the fledgling right-wing Conservative Party, Colin Craig, in a campaign speech.

Craig claimed Shanghai Pengxin, which has been at the center of previous controversial farm purchases, had agreed to buy the 13, 800-hectare Lochinver Station near the central North Island town of Taup, but the deal was being kept secret until after the election on Sept. 20 for fear of a public backlash.

"Although the deal has been agreed between the parties, and the Overseas Investment Office has received an application, the deal has not been disclosed to the public," Craig said in the published speech.

"We believe voters should be aware of what's going on behind closed doors, this is clearly an election issue," said Craig, adding, "it's time to take down the 'For Sale' sign on New Zealand. "

Within hours, Shanghai Pengxin released a statement confirming the deal, which had been agreed through its New Zealand subsidiary, Pure 100 Farm Ltd., but giving no price.

The group planned to "secure operational synergies over time" with the planned acquisition and some of its neighbouring North Island farms, purchased in 2012.

"The Shanghai Pengxin philosophy is to work co-operatively through its local subsidiaries within the New Zealand farming industry and support new investment and innovative opportunities, as well as productivity enhancement, sustainable farming practices, and building supply chain capability," said the statement.

The opposition New Zealand First party joined the Conservative Party in accusing the government of secrecy over land sales to foreign interests and promising to set up a register of such sales and to restrict them.

"They just don't care -- they're letting anyone and everyone buy our houses, land and businesses," New Zealand First leader Winston Peters said in a statement, claiming the OIO had approved sales totalling almost a million hectares over the last six years.