Google is blaming an error in its traffic routing system for a service outage on Thursday that lasted several hours.

The company said that an error in its servers at 3:48pm GMT caused several Google services to begin routing all traffic through its servers in Asia. The resulting crush of traffic caused a slowdown in Gmail, YouTube and Google search. Some users were completely unable to access the sites.

After services were restored, Google's senior vice president of operations, Urs Hoelzle, issued a statement to explain the outage, which the company estimates to have affected 14 per cent of users.

Hoelzle likened the event to an air-traffic error which would route all flights to a single airport. Because of the error, many users were left waiting in a 'holding pattern' to access the sites.

"We've been working hard to make our services ultrafast and 'always on', so it's especially embarrassing when a glitch like this one happens," Hoelzle wrote.

"We're very sorry that it happened, and you can be sure that we'll be working even harder to make sure that a similar problem won't happen again."

The is not the first time Google has experienced a major outage. A Gmail problem in April left many users unable to access their accounts, and caused some in the industry to question the viability of the service as a reliable communication tool for enterprises.