Internet search giant Google says its profits declined 20 percent in the last three months, which prompted a sharp sell-off of the company's stock on Thursday.

U.S.-based Google had planned to release its earnings report for the July-to-September period after the Nasdaq stock exchange had finished trading for the day. But the company that prints Google's financial reports inadvertently filed it with the U.S. securities agency hours ahead of time.

When investors saw Google's third quarter results, they sold the company's stock, dropping it 9 percent to $687.39. Trading in the stock was halted, with the company promising to discuss its earnings after U.S. stock markets closed for the day.

Even with the decline in earnings, Google says it still had nearly $2.2 billion in profits in the last three months. But that was down from more than $2.7 billion a year earlier, and less than stock analysts had predicted. The company report said the amount advertisers paid the company every time Internet users click on their products has been falling.