The email service is used by hundreds of millions of people across the globe.
People took to Twitter, first to report an outage, and then patchy service. Reports were coming in from Europe, the U.S., Canada,India and other parts of the world.
"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.
The error message on Gmail's landing page displayed a 500 code problem, which indicated that it was temporary, coupled with a brief note: "We're sorry, but your Gmail account is temporarily unavailable. We apologize for the inconvenience and suggest trying again in a few minutes."
The outage also affected Google+ and YouTube comments, which meant comments weren't loading at all on videos or for Hangouts across the web and mobile platforms.
It is unclear what caused the outage.
Earlier Friday before the disruptions, the Google Site Reliability Engineering team agreed to do an "ask me anything" on Reddit. Users around the world can pepper the team with questions. The event is still scheduled on the site from 3 p.m. to 4 p.m. ET.