Former Hewlett Packard chief executive Carly Fiorina announced Monday she is running for the 2016 Republican nomination, in a statement posted on Twitter.

"I am running for president," wrote Fiorina, 60, the only woman so far to join the crowded Republican presidential field.

Fiorina has a more formal announcement planned later Monday.

A former advisor to defeated Republican candidate John McCain in the 2008 White House race, Fiorina headed Hewlett Packard for six years until 2005, when she was forced to resign after the company's share price plummeted.

She ran an unsuccessful bid to unseat California' long-serving US Senator Barbara Boxer in 2010.