Carly Fiorina has quit as chairman and CEO of Hewlett-Packard after a board battle over the company's direction.

In a shock announcement made this afternoon, the company said that Ms Fiorina's departure was effective immediately.

She was quoted as saying: "While I regret the board and I have differences about how to execute HP's strategy, I respect their decision." Whether she decided to quit after failing to persuade the board of her vision, or the board offered a choice of resigning or being fired remains unclear.

The new interim chairman, Patricia C. Dunn, an HP director since 1998, said on behalf of the Board: "Carly Fiorina came to HP to revitalise and reinvigorate the company. She had a strategic vision and put in place a plan that has given HP the capabilities to compete and win. We thank Carly for her significant leadership over the past six years as we look forward to accelerating execution of the company's strategy."

The CEO role will be assumed on an interim basis by Robert P. Wayman, HP's chief financial officer.

Fiorina has been HP's CEO for six years. The company has already began looking for her replacement, it said. A press conference will be held later today. HP's quarterly results are due in a week, on 16 February, and its annual shareowner meeting will be in Chicago on 16 March.