Australian mining magnate Gina Rinehart on Thursday increased her joint offer with a Chinese company for one of the world's biggest cattle estates, to fend off a rival bid by an all-Australian consortium.

Rinehart's Hancock Prospecting and Chinese property developer Shanghai CRED raised their offer to Aus$386.5 million (US$295 million) from Aus$365 million for Australia's biggest private landowner -- cattle firm S. Kidman and Co -- days after four wealthy grazier families launched their own Aus$386 million bid.

The local families had argued their proposal was better as it did not need approval from the Foreign Investment Review Board (FIRB).

While the Kidman sale has attracted keen interest from Chinese firms wanting to secure the sprawling pastoral empire, the government has previously rejected two Chinese-led bids, citing the national interest.

The Rinehart-led bid was supported by Kidman's board, which "unanimously recommended" it to their shareholders in the absence of a superior proposal.

"Under the Hancock (joint venture) offer the core Kidman business will remain intact and the Kidman staff and legacy will be looked after," Kidman chairman John Crosby said in a statement.

Rinehart, Australia's richest woman, also pledged to buy Kidman fully if the Australian-Chinese joint offer -- in which Hancock acquires 67 percent of Kidman and Shanghai CRED 33 percent -- was knocked back by Canberra or Beijing.

"I stand behind the bid and should FIRB or PRC (China) approvals not be achieved, then Hancock will proceed with the acquisition on a 100 percent basis," Rinehart said in a statement.

"I hope this provides shareholders with significant comfort and that when they consider the offer they can do so in the knowledge that there is no FIRB or PRC execution risk, and further that we have the money to invest to properly maintain the stations and their hard-working staff."

Shanghai CRED was part of a Chinese consortium involved in the previous offers. The Chinese stake in the new joint bid, if approved, would be significantly smaller than before.

The first Chinese-led bid was rejected last November because the holdings included Anna Creek station, a rocket testing range, which was later removed from sale with Canberra citing its sensitive location.

The Australian-Chinese bid will be partly funded by the sale of Anna Creek.

Kidman, founded in 1899, holds around 1.3 percent of Australia's total land area, and 2.5 percent of the nation's agricultural land. It is currently 33.9 percent foreign-owned.

There has been growing concern in Australia about the purchase of local infrastructure and land by foreign interests.

An all-Australian consortium bought half of the nation's largest electricity network last week after Canberra rejected a Chinese bid, citing national security.