Google Inc is investigating an outage on Friday that took down Gmail, the Internet email service used by hundreds of millions of people across the globe.
Gmail service appeared to resume for some users shortly after the outage occurred.
Yahoo Inc, which runs a rival Internet service, posted a screenshot of the Gmail error page on Twitter.
"We're investigating reports of an issue with Gmail. We will provide more information shortly," the company said on its "App Status" dashboard online, which tracks the state of various Google services.
Users attempting to sign on saw a "temporary error" message and a brief note: "We're sorry, but your Gmail account is temporarily unavailable. We apologise for the inconvenience and suggest trying again in a few minutes."
The Internet search giant's Google+ social network, as well as its Youtube video service, appeared sluggish as well. Google did not respond to requests for comment.