Google Inc. reported second-quarter earnings Thursday of $6.45 US a share, below estimates.

The average earnings estimate among analysts polled by Thomson Reuters was for $6.52 per share, which would have been a 22 per cent increase from the same period last year.

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A Google banner on the display at the company's headquarters in Mountain View, Calif., in April.

Net revenue was $5.1 billion, after being widely expected to rise by about 20 per cent to $5 billion.

Google shares lost $19.32 after hours to trade down almost four per cent at $474.70 US as of 5:07 p.m. ET.

In an encouraging sign for the overall economy, marketers paid more for the online ads that generate virtually all of Google's income. People also clicked on the ads more frequently. 

Those trends indicate more companies and shoppers are feeling a little better as they recover from the worst economic downturn in more than 70 years.

With files from The Associated Press