SINGAPORE - Users of Facebook and its three popular applications faced intermittent technical issues for hours on Thursday (March 14), in what was reported to be the biggest outage suffered by the social media giant across the globe.

From Asia and Europe to the Americas and Africa, users of Facebook, Instagram, Whatsapp and Messenger complained of problems such as inability to log in, load posts or send and receive messages.

Facebook, which has more than two billion users, is still investigating the cause of the worldwide outage. But it has said the problem was not caused by a distributed denial of service (DDoS) attack, which is when hackers disrupt online services and make them unavailable to users.

Facebook first acknowledged the service disruption at about 1.50am on Thursday Singapore time.

It said on Twitter: "We're aware that some people are currently having trouble accessing the Facebook family of apps. We're working to resolve the issue as soon as possible."

About an hour later, it tweeted: "We're focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack."

Photo-sharing site Instagram said on Twitter: "We know this is frustrating, and our team is hard at work to resolve this ASAP."

By about 2pm Singapore time, Instagram announced that it was back up. Facebook was reportedly still down for some users across the globe.

In Singapore, Mr Hafiz Salahuddin, 28, was unable to see the posts of the users he followed on Instagram.

Said the 28-year-old freelance videographer: "The first thing I do when I wake up is check my socials, but for some weird reason my feed was not updating.

"I thought it was just me, but when I checked with my siblings at home, they all had the same problems."

Business users of the social media platforms were also affected. Mr Anthony Koh, 46, runs Booktique, an independent bookshop, and regularly uses Messenger and WhatsApp to answer questions from his customers or potential authors looking to self-publish.

He had been busy with an event for the past three days and had set aside time on Thursday morning to reply to the queries, but he faced issues sending and receiving messages.

"I had all these messages from my customers making inquiries, and it is a bit frustrating that I cannot do that now," said Mr Koh.

"It's very important to get back to these people as soon as I can. As business owners, we all want to respond to them on time. Already I am three days late, so this disruption comes at a bad time. I hope they understand."

The BBC called the outage the " most severe" in the history of Facebook, while the Sydney Morning Herald said it was "potentially the biggest service interruption in the social media site's history".

On the downdetector.com website, which regularly tracks the online sites and services that are experiencing issues, the Facebook disruptions seemed to be heaviest in the United States, Europe, Japan and Australia.

Mr Bryan Tan, a lawyer from Pinsent Masons MPillay who specialises in technology law and data protection, said that while disruptions do occur in these services from time to time, the length of this particular one is unusually long.

He noted that disruptions usually last between two and four hours, as a tech giant like Facebook would have systems in place to ensure that services do not take a hit for too long.

But Mr Tan said the fact that these services are just disrupted and not totally inaccessible to everyone is an encouraging sign.

"It is not a total shutdown, and just parts of the services are affected. It just might mean that one of its servers carrying these services has got a problem, and that's why you're losing part of these services," he added.

Several brand marketers tweeted that Facebook's ad-buying system was also down.

Bloomberg News reported that as of about 6.30pm US time on Wednesday (6.30am Thursday Singapore time), Facebook said it was still investigating the overall impact, "including the possibility of refunds for advertisers."

Ad sales are the company's lifeblood and persistent difficulties could be costly, said the report. Based on 2019 sales estimates, Facebook is projected to generate average daily revenue of about US$189 million (S$256 million), it added.

Similar disruptions happened in 2018. In November, Facebook attributed the disruptions to a server problem, while in September, it said there were "networking issues".

The disruptions come just a day after several Google services, including Gmail and Google Drive, experienced widespread disruption. Users had complained that they were unable to access their files or send e-mails with attachments.