NEW YORK (Reuters) - Google Inc's finance chief said on Tuesday that he plans to retire, the latest in a series of changes in the company's upper ranks but a move that some analysts said was unlikely to cause major disruptions.

Mr Patrick Pichette is leaving Google to go backpacking, the 52-year-old French Canadian announced in a lengthy post on his personal Google+ Web page on Tuesday.

Google, which dominates the online advertising business, expects to find a replacement for Mr Pichette within six months, the company said in a regulatory filing with the US Securities and Exchange Commission. Mr Pichette's retirement date has not been set and Google said Mr Pichette intends to help find a successor.

Shares of Google closed down 2.4 per cent at US$555.01 and were unchanged after hours.

Mr Pichette's decision to retire, which he said caps about 30 years of "nearly non-stop work," came as a surprise to investors, although Wall Street took the news in stride.

Mr Pichette's decision to travel after seven years at Google, appears reasonable, said Hudson Square Research analyst Daniel Ernst.

While Google is a massive company which analysts expect to generate roughly US$76 billion in revenue this year, the business is relatively straightforward, said Mr Ernst. "Any experienced CFO could slot in there and see how it all works," he said.

A former telecom industry executive who joined Google in 2008, Mr Pichette is credited by some on Wall Street for maintaining spending discipline even as Google has embarked on ambitious "moon shot" projects including self-driving cars, satellites and healthcare.

For Google, Mr Pichette's exit marks the latest change in its upper ranks. Last year, Google chief business officer Nikesh Arora left unexpectedly to become vice-chairman of Japan's SoftBank. Mr Vic Gundotra, the head of Google's social networking services, left in April 2014.

Google chief executive officer Larry Page in October turned over day-to-day management of major products and services to senior vice-president Sundar Pichai, freeing him up to focus on bigger-picture issues.

Mr Pichette said in his blog post that he decided to retire after a recent trip climbing Africa's Mount Kilimanjaro when his wife suggested they continue travelling. "I could not find a good argument to tell Tamar we should wait any longer for us to grab our backpacks and hit the road," Mr Pichette wrote, referring to his wife.

In a separate post on Google+, Mr Page wished Mr Pichette well, describing his "unconventional" farewell note as "well worth reading."