Having trouble accessing Facebook or Instagram on Wednesday? You weren't alone.

The massively popular social network started having problems at around noon Eastern time, with issues popping up across Facebook proper, Facebook Messenger and Instagram around the world. The service outage is one of the longest Facebook has ever experienced.

After being out much of Wednesday, Facebook began to come back to life early Thursday morning after midnight ET for many users.

As of publication, service had not yet been fully restored, but some users are able to access it more than others.

Rob Leathern‏, Facebook director of product, tweeted early Wednesday afternoon that officials were “also aware that people are experiencing issues with access to our ads interfaces, we'll share an update as soon as possible.”

Around 9:30 p.m. Leathern tweeted “I don’t have any update yet :(“

A Facebook spokesperson told USA TODAY that as of 10 p.m. ET, there's no update on when the service will be fully restored.

More:How to protect your Facebook credentials

Start the day smarter:Get USA TODAY's Daily Briefing in your inbox

It is also not clear what caused the issue, leading to confusion and speculation.

Roland Dobbins, an engineer with network performance firm Netscout said Wednesday that the outage was due to an accidental traffic jam issue with a European internet company that collided with Facebook and other websites.

"While not malicious in nature, such events can prove disruptive on a widespread basis," he said.

ThousandEyes, a firm that helps companies optimize their traffic, refutes Netscout's assessment, saying that in its analysis the outage appears to be an "internal" problem for Facebook "rather than a network or Internet delivery issue."

"ThousandEyes looks at issues from the user’s vantage point," Alex Henthorn-Iwane, ThousandEyes vice president of product marketing, said in a statement provided to USA TODAY. He adds that when the firm was looking into Facebook’s issues it was "not seeing any BGP changes that are affecting connectivity, packet loss or latency."

"Since Facebook uses its own backbone network, it’s not clear / we don’t have insight as to how an external transit route issue would cause a disruption within the internal Facebook network."

Some users of Facebook-owned WhatsApp reported having issues sending photos on the popular messaging app.

As with nearly every Facebook outage, users headed to Twitter with the hashtag #facebookdown quickly becoming the top trending topic in the United States.

Downdetector.com, which monitors websites, showed the company experiencing issues across a large portion of the U.S. and Europe in addition to reported problems in parts of South America, Asia and Australia.

It is not immediately clear what caused Wednesday's issue. Some users reported seeing a message saying the site was down for "required maintenance," while others were able to get the social networks to briefly load before discovering that functionality was limited.

"We’re aware that some people are currently having trouble accessing the Facebook family of apps," a Facebook spokesperson said in a statement provided to USA TODAY. "We’re working to resolve the issue as soon as possible."

In a tweet at 3:03 p.m. ET, the company reiterated that it is still working on a fix. Facebook also confirmed that the outage was not the result of any distributed denial of service, or DDoS attack.

Twitter time:What to do when Facebook and Instagram go down? Head to Twitter to tweet #FacebookDown

One of longest outages:Facebook, Instagram, WhatsApp somewhat restored early Thursday

Contributing: Jessica Guynn; Kelly Tyko

Follow Eli Blumenthal on Twitter @eliblumenthal