"We're investigating reports of an issue with Gmail. We will provide more information shortly," the company blogged.
The outage occurred just before 2 p.m. EST, leaving millions of users unable to connect with Google's Gmail servers.
Users attempting to access their Gmail accounts were greeted with a screen message saying, "We're sorry, but your Gmail account is temporarily unavailable. We apologize for the inconvenience and suggest trying again in a few minutes."
Service was reported to have been restored for most Gmail users after about 20 minutes, although there were scattered problems with sending emails and problems with Google+.
"We expect a resolution for all users in the near future," Google wrote. "Please note this time frame is an estimate and may change."
Gmail has suffered outages before in 2009 and 2012.