google parent alphabet overtakes apple
Letters spell the word "Alphabet" as they are seen on a computer screen with a Google search page in this photo illustration taken in Paris, France, August 11, 2015 Reuters

Shares Alphabet Inc. surged in after-hours trading on Monday, helping Google parent company surpass Apple Inc as the most valuable company in the world.

Alphabet shares rose after the company's quarterly profits beat analyst expectations.

Consolidated revenue rose 17.8 percent to $21.33 billion in the fourth quarter ended December 31, from $18.10 billion a year earlier, the company said on Monday.

Analysts had expected $20.77 billion. Investors who saw further room for growth in the tech giant lapped up the shares, sending the valuations higher than that of Apple, which has long been on the pedestal as the most valuable company.

The strong earnings were a result of "increased use of mobile search by consumers," as well as "ongoing momentum" in YouTube and programmatic advertising, Google Chief Financial Officer Ruth Porat said in a conference call, Reuters reported.

Chief Executive Sundar Pichai said Gmail service crossed one billion monthly active users last quarter.

In regular trading on Tuesday, Alphabet's market cap is expected to stay above Apple's current market cap of about $535 billion. Alphabet market cap had risen to roughly $570 billion in after-hours trading.

CNBC reported that the last time Google was more valuable than Apple was in February 2010. It was in 2011 that Apple surpassed Exxon to become the world's most valuable company.

Google was the most valuable company between 2004 and April 2008.

Apple is set to witness a period of slow growth in iPhone sales and a subsequent fall in revenues, reports have recently said.