Google Inc.'s stock plunged suddenly on Thursday afternoon after it released its third-quarter earnings report early, apparently by mistake.

The Web search and advertising company's stock fell $68.19, or 9 percent, to $687.30 before trading was halted to give investors a chance to digest the news. Google's report had been slated for release after the close of regular trading.

In a regulatory filing, Google said it earned $2.18 billion, or $6.53 per share, during the three months ending in September. That compared with net income of $2.73 billion, or $8.33 per share, last year.

The earnings would have been $9.03 per share, if not for Google's accounting costs for employee stock compensation and restructuring charges related to the acquisition of Motorola. Analysts polled by FactSet were expecting $10.63 per share, on average.

Revenue climbed 45 percent from last year to $14.1 billion. Excluding compensation for websites that generate traffic for Google's ads, revenue was $11.33 billion. Analysts were expecting $11.5 billion.

The strong dollar appeared to contribute to Google's miss. The company said that if foreign exchange rates had been stable, its revenue would have been $136 million higher.

Excluding this summer's acquisition of cellphone maker Motorola Mobility, Google's revenue rose 18 percent.