Google says all systems are back online after last night’s three-hour Gmail blackout. The outage hit at 8.30pm New Zealand time, and saw home and business users worldwide lose their email access.

In an online statement, the company says:

“We know that for many of you this disrupted your working day. We’re really sorry about this, and we did do everything to restore access as soon as we could. Our priority was to get you back up and running.”

Google has yet to establish the cause of the problem.

A silver lining in the cloud computing blunder: Gmail’s new offline feature is now running seamlessly (including for your correspondent), allowing users to continue to review and edit messages during the blackout.

The Gmail blackout is well-timed for Microsoft, whose CEO Steve Ballmer has recently admitted Microsoft is starting to come up against Google Apps as it competes for business (and, locally, tertiary) accounts. Flattering it with attention, Mr Ballmer has launched a series of savage attacks on Apps.

For its part, Google recently sought to reassure business customers with a 99.9% uptime guarantee for those on $US50/year Google Apps Pro accounts.