Google has started charging Gmail and Picasa users for extra online storage.

The changes to the search giant's email and photo services came just a few hours after Microsoft rolled out its Skydrive online storage service last week.

The charges, which Google took pains to stress is are for storage on top of the free allowance (1GB for Picasa, 2.8GB for Gmail), start at $20 a year for 6GB. In the first 20 minutes after the paid storage debuted, however, Google sold the 6GB bump for just $1 a year; that was quickly changed to $20.

Other plans provide an extra 25GB for $75 annually, 100GB for $250, and 250GB for $500.

In comparison, Microsoft's Windows Live Skydrive, which it has relaunched with interface changes and a name change from Live Folders, offers 500MB, about 18 percent of Gmail's free limit.

"When you reach the limit of free storage, consider this your overflow solution," said Ryan Aquino, a software engineer on Google's Picasa team, on Google's primary blog. Other Google products, such as Docs and Spreadsheets, will be able to access the shared storage "soon," Aquino added.

At one time, Google touted an "Infinity+1" strategy for Gmail's online storage space, but later settled on the current 2.8GB.

In March, rival Yahoo announced unlimited storage for its webmail service. However, Yahoo flags accounts that it thinks are being used for online storage, rather than simply storing emails.

Google was not available for comment to answer questions about the $1-per-year offering - typo or change of heart? - or why it decided to abandon Infinity+1 and charge for storage.