The bulk of the growth arises from a recent series of significant sales in Western Australia – purchases that were not covered by the ATO foreign ownership register, which only dealt with registrations up to June 30, 2016.

But a compilation of reported land sales, endorsed by agribusiness experts, suggests that even at that date Chinese investors held about 2 million hectares of farmland, calling into question the efficacy of the register.

The 1.46 million figure was almost eclipsed by just two of the largest properties: the 705,000-hectare Wollogorang and Wentworth station on the Queensland/Northern Territory border, and the 639,500-Balfour Downs and Wandanya station in Western Australia, both owned by Chinese ball bearing billionaire Xingfa Ma.

In recent months Shanghai Zenith, the local operating arm of real estate developer Shanghai CRED, has settled purchases of two large cattle stations in WA: the 200,000- hectare Mount Elizabeth station and the 189,000-hectare Yakka Munga station.

It also obtained approval to buy more than 400,000 hectares of pastoral land in WA's Goldfields region and is part of a $365 million joint bid with Gina Rinehart for the sprawling S. Kidman and Co land portfolio.

In August another company, Shanghai Zhongfu, obtained the 476,000-hectare Carlton Hill station in WA's Ord River district for about $100 million.

Other significant purchases made in recent years include Yiang Xiang Assets' acquisition of the 205,000-hectare Elizabeth Downs station in the Northern Territory, Shandong Ruyi's 80 per cent stake in Cubbie station and Dashang Group's purchase of Glenrock station in NSW for $45 million.

Fairfax Media confirmed its list of reported land sales with Danny Thomas, regional director of agribusiness with CBRE, who personally oversaw several of the largest purchases of land by foreign investors.

The ATO said it did not comment on individual land holdings and acknowledged its register relied heavily on self-registration, with penalties up to $9000 applied for failure to do so – though it had not yet issued any. It also stressed the register only counted account registrations before June 30.

"Significant steps have been taken to make sure that foreign investors are aware of their obligations to register their agricultural land interests," an ATO spokesperson told Fairfax Media.

"The ATO has commenced a compliance program to ensure that foreign investors who hold Australian agricultural land are meeting their obligations.

"The ATO has not issued any penalties for failure to register as yet and [is] utilising its data sources to identify foreign persons who have failed to register and to detect patterns, trends and drivers of non-compliance."

Released in September, the ATO register was welcomed by the Turnbull government for showing "just 13.6 per cent" of agricultural land was held by foreign investors, and only 0.38 per cent by China.

China placed fifth behind Britain, the US, the Netherlands and Singapore. But at 3 million hectares, China would rise to third, assuming the ATO figures for the other countries are correct.

The register was already criticised by Coalition figures who wanted a more detailed report on who owns what. But the ATO said that would contravene tax laws.

Tim Lane, national director of property advisory Herron Todd White, agreed the ATO figure seemed to be incorrect. He said an estimate of 2 million hectares by June 30 and 3.2 million hectares today was closer to the mark.

"The land areas don't appear to be in line with what we'd understand them [to be]," he said. "It's pretty clear you can see it's not the correct number."

Mr Lane said the register's main flaw was that it treated all hectares as equal when some, such as Queensland's Cubbie Station, were vastly more productive and profitable than others. "It's a good start [but] we've got to build more confidence in the data," he said.

Executive director of the Australian Farm Institute Mick Keogh said the usefulness of the register was limited because investment was "a constantly moving feast".

Mr Thomas said the boom in Chinese buying activity in 2016 reflects increased interest from foreign investors the world over. "The market is as active at the moment as I've seen it in my professional career," he said.

The register will be updated next year, covering registrations up to 30 June 2017. Chinese investors are also thought to be behind the purchase, through South Australian advisory firm Agrify, of the 1 million-hectare SAWA Pastoral Co, which is awaiting government approval.