The world's favourite internet search engine, Google, has joined the corporate super-league with a market value which ranks among America's top five companies.

Just a decade after its creation in a Stanford University dormitory, the Silicon Valley firm's capitalisation reached $219bn on Tuesday - overtaking healthcare titan Proctor & Gamble to place it fifth on the US stockmarket.

Only ExxonMobil, General Electric, Microsoft and the telecoms company AT&T are larger than Google.

Its shares powered past yet another milestone today as they touched $700 for the first time, less than a month after reaching the $600 mark. By mid-morning in New York, they were up $5.27 to $700.04.

Google's growth spurt has been driven by seemingly unstoppable profits - the company's recent third-quarter earnings showed a 46% leap in net income to $1.07bn. Experts cite its leadership in online maps, videos, news and finance - all of which are considered so far "under-monetised" but are thought to offer huge potential for advertising-driven revenue.

Todd Greenwald, an analyst at Nollenberger Capital in San Francisco, said: "Could they be bigger? Certainly. Frankly, the market's only just realising the vast amount of earnings power and is valuing Google appropriately."

The soaring share price means Google's two 34-year-old founders - Sergey Brin and Larry Page - have paper fortunes of more than $20bn each.

The pair only take salaries of $1 a year but receive more than $1m in annual bonuses. They have shown a taste for jetset living - they have refurbished a former Qantas Airways 180-passenger Boeing 767 as a "party plane" with twin staterooms, a dining room and showers and have won permission to keep it at a usually restricted Nasa base in California. Google is 10 times as valuable as America's biggest carmaker, General Motors, and is worth 30% more than the world's largest drugs firm, Pfizer. Long established "old economy" brands pale into comparison - Coca-Cola's capitalisation is just $142bn, while McDonald's can only command a value of $70bn.

Most industry followers believe that the only way is up for Google. The information service Bloomberg reported that out of 37 analysts tracking the company, 33 recommend buying the shares and the other four rate the stock as a "hold".

Google accounts for 56% of all searches on the internet according to the online research firm Comscore. In Britain, Google is visited more than any other website with 28.6 million unique users in September - reaching 89% of all UK internet users.

Long-term critics of Google question the company's cost control - its payroll has grown rapidly to 16,000 - and point to litigation from broadcasters over alleged rampant copyright abuse at Google's YouTube arm. But Mark May, an internet analyst at Needham & Company, wrote in a recent note: "We continue to view Google as a core holding and believe the company's strong brand loyalty, the business's substantial free cashflow potential and the team's track record of innovation will lead to further gains."

Google is shortly expected to reveal plans for a mobile phone to take on hi-tech competitors such as Apple's iPhone. The Google-powered phone is intended to make it easier to access the company's most popular features through a handset - including YouTube, maps and Gmail email.

Competitors have struggled to keep up. Yahoo!, which ranks second among internet searches, has lost ground and recently parted company with its chief executive amid criticism over its drifting strategy.