Facebook was down briefly Thursday morning, causing millions of users worldwide to be without access to the hugely popular social media website.

Users in the United Kingdom, Israel, the U.S. and more were affected. The outage occurred around 4 a.m. ET, so many users in the U.S. didn't even notice. But elsewhere in the world, it was during a more popular time to use the social network.

Those in areas where the site was down received the message "Sorry, something went wrong. We're working on getting this fixed as soon as we can." This frustrated many users and they described their frustrations on Twitter.

Quickly the topic #facebookDown became trending worldwide.

Twitter user Craig Wallace said: "Facebook down? Stay tuned for emergency broadcasts & zombies in the streets. This is how it ends."

Another Twitter user, Jason Webster, said:

"Chill everyone it's back. Shall we all get Tshirts made saying "I survived the Facebook apocalypse" #facebookdown" 

Michael Suibne said on Twitter: "I saw overturned cars, plumes of smoke in the distance. A woman lay on the curb asking for Candy Crush Hearts. It was madness. #facebookdown"

"Late last night, we ran into an issue while updating the configuration of one of our software systems," a Facebook spokesman said. "Not long after we made the change, some people started to have trouble accessing Facebook. We quickly spotted and fixed the problem, and in less than 30 minutes."

Facebook said this doesn't happen often and that they were able to learn from the experience.

"This doesn't happen often, but when it does we make sure we learn from the experience so we can make Facebook that much more reliable," the company spokesman said. "Nothing is more important to us than making sure Facebook is there when people need it, and we apologize to anyone who may have had trouble connecting last night."

Facebook, which connects users to their friends, family and even celebrities, has almost 1.3 billion users. Eighty percent of those users are outside of North America. It is not the first time the site has gone down. Normally when it occurs, Facebook quickly fixes the problem.

Following a 2010 outage, Facebook made a blog post explaining why the site went down. During that outage, Facebook servers were down for two and a half hours.