WASHINGTON (AFP) - A US debt default would cause serious economic repercussions, including "deeply damaging" financial markets,

Treasury Secretary Jack Lew warned lawmakers on Thursday a week before a deadline to raise the US borrowing limit.

"If Congress fails to meet its responsibility, it could be deeply damaging to the financial markets, the ongoing economic recovery, and the jobs and savings of millions of Americans," Mr Lew testified before the Senate Finance Committee.

"If Congress does not act and the US suddenly cannot pay its bills, the repercussions would be serious."