US national debt crosses $40 trillion threshold

Total US debt has topped $US40 trillion ($A56 trillion) for the first time, the Treasury Department says, drawing fresh warnings a fiscal crisis is brewing as ballooning costs for social safety-net programs and interest payments far outstrip revenues held back by tax cuts.

The Treasury's latest daily cash and debt balances statement showed total public debt outstanding at $US40.047 trillion, a total that includes Treasury securities held by the public of $US32.266 trillion and intra-governmental debt holdings of $US7.782 trillion.

The federal government's IOU has now more than doubled in less than a decade, from $US19.95 trillion when President Donald Trump was sworn in for the first time in January 2017.

Roughly one-third of that increase occurred during two years of frantic government borrowing to fund the COVID-19 pandemic responses undertaken by Trump and former President Joe Biden, while the fiscal policy choices of both presidents combined with long-running tax-and-spending imbalances to account for the rest.

Budget watchdog groups have been anticipating the crossing of the threshold for weeks and have issued stark warnings that a full-blown debt crisis could erupt unless politicians confront an unsustainable fiscal outlook and raise taxes, cut spending or both.

"Forty trillion dollars of debt doesn't exist solely on the government's ledgers; it is felt throughout the economy and finds its way to the pocketbooks of people one way or another," said Maya MacGuineas, president of the nonpartisan Committee for a Responsible Federal Budget.

"The more we borrow, the more we exacerbate inflation, squeeze out other priorities in the budget, and leave ourselves vulnerable to emergencies at home and turmoil abroad."

She noted the $US40 trillion figure was reached less than five months after debt reached $US39 trillion, and has quadrupled in less than 20 years after taking until 1981 to reach $US1 trillion for the first time.

"It is staggering how predictable the fiscal decline of a global power can become," MacGuineas added.

Global US creditors may already be growing wary.