Google Executive Chairman Eric Schmidt plans to sell nearly 42 percent of his stake in the company, according to a stock filing from Google with the US Securities and Exchange Commission.

Schmidt will be unwinding 3.2 million shares of Class A common stock through a stock trading plan which will be worth $2.5bn (£1.6bn, €1.9bn).

He owns about 7.6 million shares of Class A and Class B stock which accounts for 2.3 percent of Google's outstanding shares.

The sale will be spread over a year to avoid any impact on the company's share price. Google shares closed at $781.26, down $4.11 in after-hours trading on Friday.

Google said the stake sale will provide Schmidt "individual asset diversification and liquidity". However, no reason for Schmidt's decision was given.

"My speculation is that Eric's relationship with Google is evolving. I would assume that as he decides he wants to diversify away from Google - both his career and financially - he's got ideas of what he would like to do with some of his funds," Needham & Co analyst Kerry Rice told Reuters.

Schmidt stepped down as the chief executive of Google in April 2011, paving way for the co-founder of the company, Larry Page, to take the helm.

Schmidt made headlines recently with his visit to North Korea and remarks about China. He has called China the "most sophisticated and prolific" hacker of foreign companies in a soon-to-be published book entitled The New Digital Age.