The United States' federal government shutdown could endanger the fragile world economy, Prime Minister David Cameron warned on Tuesday.

"It is a risk to the world economy if the United States can't properly sort out its spending plans and its deficit reduction plans," Cameron told BBC radio after the US Congress failed to agree a budget, forcing the first federal government shutdown in 17 years.

Economists have warned that the shutdown, forcing 800,000 federal workers to go on leave and closing museums and national parks until the row is resolved, could slow growth in the world's largest economy.

Cameron added: "I think also it's a reminder to us here that you have to have a multi-year, long-term plan for getting deficits down."