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. 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 wouldve 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 percent of Google's users encountered problems with the Internet's No. 1 search engine. Those outages lasted about an hour.