NSW needs an independent food authority to co-ordinate all aspects of food production and access to healthy food, says a coalition of producers, food security experts, permaculture gardeners, health workers and nutritionists.

The Sydney Food Fairness Alliance and allied groups called on the state government to create an independent food policy council to work to ensure the state's food security, which is under threat from climate change, water shortages and the loss of arable land to housing and mining uses.

Food security traverses health, primary industries, planning, environment, water and other portfolios, requiring a whole-of-government approach, the group said.

David Mason, an urban agriculture expert, told an audience of MPs and others at Parliament House yesterday that Australia produces enough food for about 70 million people a year, well in excess of its population of 22.4 million. But the global population is growing by about 70 million each year, which means the world needs to produce that much more food every year to feed itself. Our agricultural system was reaching its limits, he said.

Key planks of a food policy would include locking up prime farmland and water supplies to protect them from competing land uses, and finding ways to make the food supply chain more sustainable and resilient, said Jane McIvor from the Macarthur Future Food Forum