Facebook has been down for some users for nearly a full day. 

The social network has been having issues since around 9 a.m. PT Wednesday, according to tracking site Down Detector. At the time of this publication, 21 hours later, many users have regained full access, but Facebook still hasn't given the all clear.

Reached for comment Thursday, a Facebook representative said the company had nothing to add beyond its statement from Wednesday. 

"We're aware that some people are currently having trouble accessing the Facebook family of apps," a Facebook spokesperson said in an email. "We're working to resolve the issue as soon as possible." 

Instagram was also down for many hours, starting at around the same time. However, Instagram's official Twitter account announced the platform was back in action at 9:41 p.m. PT time on Wednesday. Facebook's official Twitter account has given no such update. 

Users throughout the day Wednesday posted on Twitter that they were seeing a message saying Facebook was "down for maintenance." Other users trying to post status updates on Facebook, including CNET staff, got error messages saying "something went wrong." 

The outage affected users in the US, Europe, South America, Australia and Asia, according to a map by Down Detector. Users of Facebook-owned WhatsApp also reported they were having trouble sending photos on the app. Virtual reality company Oculus, also owned by Facebook, reported that its users, too, were having trouble accessing and using the platform. 

Facebook, which makes money from selling ads, was having issues with its ad products as well.

Facebook hasn't revealed the cause of the outage, but said in a tweet Wednesday that the issue wasn't a cyberattack known as a distributed denial-of-service (DDoS) attack, where hackers try to crash a site by flooding it with too much traffic. 

This isn't Facebook's first outage. In November the social network went down in a mishap caused by a test the company was running. That outage lasted about 40 minutes. That same month, Facebook and Instagram were down for hours because of what Facebook said was a server configuration. This is, however, the longest outage in Facebook's history. The previous record-holding outage occurred in 2008, when Facebook had just 125 million users.

Originally published March 13, 10:22 a.m. PT.
Updates, 10:46 a.m.: Adds comment from Facebook; 12:18 p.m.: Includes tweets from Facebook; 1:23 p.m.: Adds background on what areas were affected, and info on WhatsApp; 5:06 p.m.: Includes the length of the outage and more info on WhatsApp; 11:19 p.m.: Adds Instagram tweet and length of Facebook's outage; March 14: Notes that Facebook still hasn't said if the outage is over for all users.