By 2030, the average cost of key crops will increase by between 120% and 180%, the charity forecasts.

Half of that increase will be caused by climate change, Oxfam predicts, in its report Growing a Better Future.

It calls on world leaders to improve regulation of food markets and invest in a global climate fund.

"The food system must be overhauled if we are to overcome the increasingly pressing challenges of climate change, spiralling food prices and the scarcity of land, water and energy," said Barbara Stocking, Oxfam's chief executive.

In its report, Oxfam highlights four "food insecurity hotspots", areas which are already struggling to feed their citizens.

The World Bank has also warned that rising food prices are pushing millions of people into extreme poverty.

In April, it said food prices were 36% above levels of a year ago, driven by problems in the Middle East and North Africa.

Oxfam wants nations to agree new rules to govern food markets, to ensure the poor do not go hungry.

Ahead of the UN climate summit in South Africa in December, world leaders are called to launch a global climate fund so that people can protect themselves from the impacts of climate change and are better equipped to grow the food they need.