Google says its first quarter profit rose 32 per cent from a year ago to $US3.45 billion ($A3.70 billion), in results below most Wall Street expectations.

Chief executive Larry Page hailed “another great quarter” for the tech giant, with revenue of $US15.4 billion, up 19 per cent year on year.

“We got lots of product improvements done, especially on mobile. I’m also excited with progress on our emerging businesses,” Page said in a statement on Wednesday.

But Google shares tumbled 5.7 per cent in after-hours trade to $US556.64, suggesting that the growth was below investor forecasts.

Earnings per share amounted to $US6.27 compared with analyst projections of $US6.40. Analysts also expected a higher revenue figure of $US15.5 billion.

Google remains the world’s most important search engine, which generates large amounts of advertising revenues.

But it is increasingly focusing on the Android mobile system and new technologies, highlighted by its recent acquisitions of Nest Labs and drone maker Titan Aerospace.

The earnings report showed a 26 per cent rise in “paid clicks”, a key figure for Google’s advertising and revenues, growth slightly lower than the 29 per cent expected by analysts.

The price per click fell one per cent in the quarter and nine per cent over the past year.

Analysts say this reflects a growing move to smartphones, where clicks produce lower revenues than on traditional PCs.