Google identifies Amazon as its biggest rival

But Mr Schmidt pointed out that competition in the online world "isn't always like-for-like".

"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," he said.

"They are obviously more focused on the commerce side of the equation, but, at their roots, they are answering users' questions and searches, just as we are."