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The executive chairman of Google owner Alphabet is to step down in January, the company has announced.

Eric Schmidt, who has been with the tech giant since 2001, will remain on the board as a technical adviser on science and technology issues.

Mr Schmidt has played a key role in the development of Google from a small California start-up to the global business it is today.

Alphabet said it expected to appoint a non-executive chairman.

In a statement Mr Schmidt said "the time is right in Alphabet's evolution for this transition".

He added that in recent years he had spent a lot of his time on science and technology issues and philanthropy and he would expand that work.

Google was founded as an internet search company in 1998 by Larry Page and Sergey Brin.

Mr Schmidt joined the company as chief executive in 2001, becoming chairman in 2011.

In 2015 Google restructured and the new parent company was called Alphabet with Mr Schmidt becoming chairman.

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Alphabet has more than 70,000 employees worldwide, and owns Google Search, Maps, Ads, Gmail, Android, Chrome, and YouTube.

Joe Beda, chief technology officer of technology firm Heptio and a former Google employee, said: "He helped them mature into the powerhouse business it is today without throwing away the uniqueness that was Google during those early days."

Alphabet board member John Hennessy said Mr Schmidt had been "tremendously effective and tireless in guiding our board, particularly as we restructured from Google to Alphabet".

'Other Bets'

Google still makes up the most of Alphabet's revenue and income.

However, the group also includes the so-called Other Bets unit, which includes the Waymo driverless car business and the Project Loon WiFi-enabled weather balloon venture.

Mr Schmidt said the Alphabet structure was "working well", and "Google and the Other Bets are thriving".