SAN FRANCISCO: Google Inc's Gmail service was knocked offline on Tuesday in an outage that the company said affected a “majority” of its millions of email users, including consumers who get Gmail for free and businesses that pay for a version for their employees.

The disruption, which lasted under two hours, was a reminder of the growing dependence on Google's technology. The free version of Gmail is the world's third most-popular e-mail programme with some 149 million users worldwide in June, ranking behind the free e-mail services offered by Microsoft Corp and Yahoo Inc, according to data from comScore Inc.

Tuesday's disruption led tens of millions of Gmail users to get an “Unable to reach Gmail” error message as their computers tried repeatedly to reconnect to the service. Google said it had taken some of Gmail's servers offline for routine maintenance, and underestimated the load that would place on other computers responsible for directing traffic to the appropriate Gmail servers.

Google said it was alerted to the failures within seconds. It said it has added capacity and made other changes to prevent similar incidents in the future. A separate outage on Monday had wiped out e-mail to a “small subset” of users.

Though occasional disruptions are common, widespread outages involving Google's services are rare. They are becoming a bigger threat to Google as it tries to sell more of its services to businesses.

Businesses are increasingly leaning on Google's services because they are delivered over the Internet instead of being managed in-house. That can save companies money and buy them more storage than they could otherwise afford. But many corporations are skeptical about outsourcing such critical tasks.

Google argues that Web-based services are more reliable than those handled in-house, but big outages like Tuesday's add another challenge to selling to reluctant businesses.

Google says more than 1.75 million businesses use Gmail as part of Google Apps, which is Google's answer to business software from Microsoft Corp. It's a key part of Google's strategy to inject its brand deeper into corporations. Google Apps costs $50 per user per year.

As usually happens with hiccups in popular Web-based services, the Gmail glitch touched off a flurry of posts to social-networking Web sites from frustrated Gmail users wondering if others were having the same problem.

“Omg thank God I was at work!!! I would've gone mad!'' one Twitter user wrote. Some favored snark. “Minute 30 of Gmail outage. The cities are in flames and people eating pets to survive. To future generations: we meant well,'' another user tweeted.

The last major outage at Google happened in May, when millions of people were cut off from Google's search engine, e-mail and other online services after too much traffic was routed through computers in Asia.

About 14 per cent of Google's users encountered problems with the Internet's No. 1 search engine. Those outages lasted about an hour.