Interest in Google's new social networking service has exceeded not only the company's expectations but its ability to keep up with the new demand.

Google+ is no longer taking new users, even if they received invites to join.

Late on Wednesday night, Vic Gundotra, a senior vice president of Social for Google, posted on the Google+ network that the company has been overwhelmed with interest and had to stop taking new users.

"We've shut down invite mechanism for the night," Gundotra posted. "Insane demand. We need to do this carefully, and in a controlled way. Thank you all for your interest!"

The shutdown means people can't invite anyone else to join Google+ right now -- and even people who already had been invited onto the network can't get in.

"Already invited? We've temporarily exceeded our capacity. Please try again soon," was the message one would-be user who was invited got today.

A Google spokeswoman said she didn't have any information on how many people have signed up to use Google+ or how many invitations have been sent out. She did say that the invitation process will be opened and closed periodically as the company works on getting the network ready for its big public release.

"We launched Google+ in a field trial in order to test the product out and gather more feedback," the spokeswoman wrote in an email to Computerworld. "As part of the field trial, we may open and close Google+ to new users at any time. We're thrilled so many people are interested in trying out a new approach to online sharing."

She added that the goal of the field trial is see exactly how Google+ works outside of the company's own walls. And Google also is looking for user feedback and time to fix any bugs they may find.

The spokeswoman did not offer details on what bugs may have been found, and she could not say when Google+ will be released publicly.

Ezra Gottheil, an analyst with Technology Business Research, said a limited field test may actually frustrate people who want to get on the network and try it out, but can't.

"It makes [Google] seem like they're not ready for primetime," said Gottheil. "You can't really use a social network unless you have a social network.... They get one chance to get attention, but I think [Google] would have been better off with something like, "Try it with one small circle, limited to 10 or 20 or whatever members, instead of something so limited."

Google took the wraps off its new Google+ project on Tuesday, after months of Internet buzz that Google was working on a social network that could take on Facebook, now the largest social net in the world. Facebook has more than 500 million users.

When Google launched its network, the company didn't open it up to everyone. Instead, a small group of people, including some journalists, were invited to try out Google+ and invite 15 others to join them.

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin or subscribe to Sharon's RSS feed . Her e-mail address is sgaudin@computerworld.com.