A US intelligence portrait of the world in 2030 predicts that China will be the largest economic power, climate change will create instability by contributing to water and food shortages, and there will be a "tectonic shift" with the rise of a global middle class.

The National Intelligence Council's Global Trends Report, published every five years, says the world is "at a critical juncture in human history".

The report, which draws in the opinion of foreign experts, including meetings on the initial draft in nearly 20 countries, paints a future in which US power will greatly diminish but no other individual state rises to supplant it.

"There will not be any hegemonic power. Power will shift to networks and coalitions in a multi-polar world," it says.

The report offers a series of potential scenarios for 2030. It says the best outcome would be one in which "China and the US collaborate on a range of issues, leading to broader global co-operation". It says the worst is a world in which "the US draws inward and globalisation stalls."

"A collapse or sudden retreat of US power probably would result in an extended period of global anarchy; no leading power would be likely to replace the United States as guarantor of the international order," it says, working on the assumption that the US is a force for stability - a premise open to challenge in Iraq and elsewhere in the Middle East and beyond.

The NIC report draws a distinction between what it calls "megatrends" - things that are highly likely to occur - and "game-changers", which are far less certain. Among the megatrends is growing prosperity across the globe.