File photo: REUTERS/Regis Duvignau.

Facebook Inc struggled to restore its services fully on Thursday after a 17-hour partial outage made the world's largest social network inaccessible to users across the globe, driving a wave of online complaints.

The number of reports on the crowd-sourced DownDetector website - one of the internet's most used sources of numbers on outages - peaked at just over 12 000, gradually falling to a couple of hundreds by early Thursday.

But with thousands of users complaining on Twitter under the hashtag #facebookdown, a number of media reports put the number affected in the millions.

The BBC and a handful of other media outlets said it was the platform's longest ever outage. Reuters was not immediately able to verify those claims.

Facebook representatives took to Twitter to update users on the problems.

A Facebook spokesman, asked by Reuters for more details, would only repeat the company's initial statement on the outage on Wednesday, saying that it was working to resolve the issue as soon as possible.

Instagram, Whatsapp and Facebook apps were down for much of Wednesday, although the photo-sharing social network said it was back up early on Thursday. Facebook was yet to provide an update on its other services.

"Anddddd... we're back," Instagram tweeted along with a GIF image of Oprah Winfrey screaming in excitement.

Social media users in some parts of the United States and Europe as well as in Japan were hit by the disruption, according to DownDetector's live outage map https://downdetector.com/status/facebook/map.

"Ya'll, I haven't gotten my daily dosage of dank memes and I think that's why I'm cranky. #FacebookDown," tweeted Mayra Mesina, a Facebook user.

The Menlo Park, California-based company, which gets a vast majority of its revenue from advertising, told Bloomberg that it was still investigating the overall impact "including the possibility of refunds for advertisers."

On Twitter it also said that the matter was not related to a distributed denial of service (DDoS) attack.

In a DDoS attack, hackers use computer networks they control to send such a large number of requests for information from websites that servers that host them can no longer handle the traffic and the sites become unreachable. 

Reuters