If you have been holding onto a Google+ invitation, now may be the time to use it.

After shutting down the invitation process late last week because of "insane demand" from people eager to try out Google 's new social network, the company began to allow new members in last night.

But this is far from an official launch of the site, which is competing directly with Facebook , that would open it up to everyone.

Dave Besbris, engineering director for Google+, said in a blog post on the site Wednesday night that Google is only re-opening the invitation mechanism for a short time.

"Things are going well with the systems right now so we feel comfortable enough to open up invites for a brief period," he wrote. "Our goal is to double the user base in the field trial."

Besbris noted that Google is not commenting on how many people have been allowed in to try out Google+ .

"I wanted to take a moment to explain why we're growing the system slowly," he added in his post. "First, we want to make sure our infrastructure scales so the service remains fast and reliable. Second, we want to ensure that bugs are fixed while there are still a relatively few people in the field trial."

He also warned users not to send out mass invitations. Google is "throttling invites" so users are likely to have more success if they only try inviting a handful of people.

When Google closed the invitation process last week, people weren't allowed to invite anyone new, and even people who already had invitations were not allowed access to Google+.

The company said last week that they expect the invitation process to be periodically opened and closed as they work through field trials.

No time has been given for when the social network might officially open to the public.

There has been enough buzz about Google+ that people have been frustrated with the company's slow rollout of the platform. Some people have taken advantage of that frustration, and have tried to sell invitations on eBay.