SAN FRANCISCO (REUTERS) - Google Inc's internet business revenue grew 19 per cent in the first quarter, falling short of Wall Street targets as the price of its online ads continued to decline.

Shares of Google were down 5.7 per cent at US$525 (S$656) in after-hours trading on Wednesday.

The number of "paid clicks" by consumers on Google's ads increased by 26 per cent year-on-year in the first quarter, while the average "cost per click" declined 9 per cent. Google's core Internet business revenue was US$15.42 billion in the first quarter, versus US$12.95 billion in the year-ago period.

Google posted US$3.45 billion in net income, or US$5.04 per share, in the three months ended March 31, compared to US$3.35 billion, or US$4.97 per share, in the year-ago period. Excluding certain items, Google said it earned US$6.27 per share.

Google reported a US$198 million net loss from "discontinued operations," which includes the Motorola smartphone business.

Google announced plans in January to sell the money-losing business to China's Lenovo Group for US$2.91 billion.