A CAMPAIGN to block foreign farm ownership until a national interest test is conducted receives support from Greens and some Independents.

Greens leader Christine Milne, independents Bob Katter and Nick Xenophon, and Labor backbencher Kelvin Thomson have thrown their weight behind the campaign by Ausbuy, an organisation that promotes Australian-owned and grown food.

Ausbuy yesterday presented 50,000 signatures from people calling for a moratorium on the sale of Australian farmland to foreign investors to the cross-party group.

Senator Milne said Australia was falling behind other countries that were securing their long-term food prospects.

"Extreme weather events have meant that many countries won't be able to buy food in the open market.

"So countries are outsourcing food production and sending that food back in (home)," she told reporters.

Mr Thomson said countries that blocked foreign investment of prime agricultural farmland weren't being racist or xenophobic.

"This is them displaying an enlightened regard for their own self-interest and for their future," he said.

Senator Xenophon said Australia should mimic the stance of other countries, including New Zealand, in imposing tighter restrictions on foreign farmland investment.

"Despite my name, I'm not xenophobic," he told reporters.

"I'm not blaming the Chinese, Saudi, Qatari or Japanese investors for investing in our prime agricultural land.

"They're actually being smart and looking at the long term, and we're not."

Mr Katter said imported fresh food should carry labels like the health warnings on cigarettes if they contain unsafe chemicals.