Dan Farber/CNET

Google has competitors in all of tech's largest companies, but the one former CEO Eric Schmidt is watching the most is Amazon.

Schmidt, who now serves as chairman of Google's board of directors, said Amazon is his company's No. 1 rival when it comes to search, thanks to Amazon's active e-commerce site.

"Many people think our main competition is Bing or Yahoo," he said during a visit to a Native Instruments, software and hardware company in Berlin. "But, really, our biggest search competitor is Amazon. People don't think of Amazon as search, but if you are looking for something to buy, you are more often than not looking for it on Amazon."

Schmidt noted that people are looking for a different kind of answers on Amazon's site through the slew of reviews and product pages, but it's still about getting information. Google is the most popular site on the Internet, receiving about 233.1 million unique visitors for all its sites, according to ComScore's media report for the month of August. Amazon ranks sixth on the list, attracting roughly 172 million unique visitors.

Google has been trying to build out its e-commerce services to try to lure consumers back to its pages. The company partnered with retailers last year to offer same-delivery services of goods in the San Francisco Bay Area, before expanding to other cities this year. After Amazon made a big splash last December with the unveiling of its drone delivery program, Google followed with a summer announcement of its own unmanned aircraft delivery service project.

While Schmidt focused only on Amazon's e-commerce prowess, the Seattle-based company has been tip-toeing into Google's turf as well. Amazon announced in August that it was shelling out $1 billion to acquire game-streaming service Twitch, a company that reportedly had been in talks with Google. Additionally, the company is said to be building out an ad network platform, which has long been Google's bread and butter.

The bottom line, Schmidt said in Berlin, is Google needs to keep innovating or "someone else will innovate around us -- leaving us obsolete over time."