Google's Gmail suffered a worldwide crash for nearly two hours Tuesday after it took some servers offline for maintenance, a widespread outage the California-based company called a "Big Deal" in a blog explaining the service failure.

"We know how many people rely on Gmail for personal and professional communications, and we take it very seriously when there's a problem with the service," wrote Ben Treynor, vice president of engineering for Gmail, in a blog post late Tuesday.

Google said the outage occurred when it took some of its mail servers offline for routine maintenance. Recent structural changes were already placing a heavy load on its routing servers, which direct Web queries to the right Gmail servers for response, and the extra burden caused an overload.

The outage was traced "within seconds," Treynor wrote, but the 100 minutes of downtime was an enormous inconvenience for Gmail's approximate 150 million users, who were shut out of the service beginning at about 1 p.m. EDT.

Google apologized for the problems, saying "we're committed to keeping events like today's notable for their rarity."

The popular mail service was hit with similar problems in February, March, April and May.