Shortly before 5:45pm UK time, many Gmail users received error messages on their accounts, meaning they could not send or receive email or access their inboxes.
The search giant said it was "investigating reports of an issue" with its popular email service, which was partially restored by 6.30pm.
A subsequent statement issued as services were being restored said "We're aware that some users are experiencing an error when accessing their Gmail. We are working on a resolution and apologize for the inconvenience. Thanks for your patience."
Google first acknowledged the problems via their apps status dashboard at 5.42pm and tweeted that they had received several reports of errors.
At 6.24pm the Gmail status was updated to read "Google Mail service has already been restored for some users, and we expect a resolution for all users in the near future. Please note this time frame is an estimate and may change."
Many users, however, were still reporting problems accessing their account after 7pm.
Gmail, which is one of the world's most popular email services, claims more than 350 million active accounts but said overall fewer than 2 per cent of its users were affected worldwide.
The service is currently being upgraded to a more efficient network running the 'Openflow' open source standards. A Wired report claimed "hundreds of engineers" were working on the project, and that Google was even building some of its own network switches.
Gmail and Google's Apps have been widely praised for their recent improvement, with Gartner saying last year that "Gmail is ready to tackle Outlook".
