The future of food supplies is under "severe threat" because of the number of animal and plant species disappearing, a United Nations report has found.

People are depending on fewer species for food, said the UN's Food and Agriculture Organization (FAO), leaving production systems susceptible to shocks like pests, disease, droughts and other extreme weather events.

Although about 6000 plant species can be used for food, less than 200 varieties are widely eaten and only nine make up most of the world's crop production.

"The loss of biodiversity for food and agriculture is seriously undermining our ability to feed and nourish an ever-growing global population," FAO head Jose Graziano da Silva said in a statement.

"We need to use biodiversity in a sustainable way, so that we can better respond to rising climate change challenges."

By analysing data from 91 countries, the FAO said there was "mounting evidence" the world's biodiversity was under "severe threat" due to pollution, badly managed water and poor land use policies.

Climate change will become an increasingly large threat to biodiversity by 2050, adding to damage from pollution and forest clearance.

From insects to seagrass, crustaceans and fungi, nearly a quarter of nearly 4000 wild food species are in decline, with the hardest hit regions being Latin America, Asia and Africa, the report said.

Global food production must become more diverse and include species that are not widely eaten but could be better equipped to withstand hostile climates.

"Compounded by our reliance on fewer and fewer species to feed ourselves, the increasing loss of biodiversity for food and agriculture puts food security and nutrition at risk," Graziano da Silva said.

Diversification could also help fight malnutrition globally by bringing little-known but highly nutritious foods into the mainstream.

One in nine people already do not have enough food and the world population is expected to reach 9.8 billion by 2050.