Here's an update from Gmail blog.
Update (2:37 pm): We've fixed the issue, and Gmail should be back up and running as usual. We're still investigating the root cause of this outage, and we'll share more information soon. Thanks for bearing with us.With that, hope everything okay with the million of Gmail users.
We know many of you are having trouble accessing Gmail right now — we are too, and we definitely feel your pain. We don't usually post about minor issues here (the Apps status dashboard and the Gmail Help Center are usually where this kind of information goes). Because this is impacting so many of you, we wanted to let you know we're currently looking into the issue and hope to have more info to share here shortly. If you have IMAP or POP set up already, you should be able to access your mail that way in the meantime. We're terribly sorry for the inconvenience and will get Gmail back up and running as soon as possible.