Google has apologised to customers after millions of users were shut out of their Gmail accounts. A global outage saw the system go down for two-and-a-half hours from about 9.30am.

An estimated 127 million people have Gmail accounts – making it the third most popular email provider after Yahoo and Hotmail, according to the internet data company comScore. Google stressed the loss of service was an "unusual occurrence".

A statement by the Gmail site reliability manager Acacio Cruz read: "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 added that its engineers were still trying to establish the root cause of the problem. A spokesman for the internet giant said: "The problem is now resolved and users have had access restored."