According to outage tracker Down Detector, the service was having issues globally.

Key hotspots for user complaints appear to be focused in central Europe, Southeast Asia, South Africa and China.

WhatsApp users in the UK were also reporting issues.

The Facebook-owned app is one of the world's most popular mobile messengers in the world.

Around 1.5billion users log on to the app every single month.

Users took to Twitter to complain about their confusion over the gaffe.

The confusion was made worse by the lack of any official announcement over an outage from WhatsApp HQ.

Reports of an outage were still trickling in after 8am on Thursday morning.

But it seems like the problem has now largely been resolved for most WhatsApp users.

WhatsApp has yet to make an official announcement about what went wrong.

It's been a bad few weeks for Facebook in terms of their service operations.

Back on June 6, Facebook-owned Instagram stopped working properly for a large number of users around the world.

After much user frustration, Facebook eventually admitted that there was a bug with the Android version of its Instagram app.

Then just two days ago, Instagram went down for users globally again.

A curious bug meant that app users weren't seeing new photos in their feed, effectively making the app redundant.

Other users reported that they were unable to leave comments on existing photos, too.

WhatsApp is a hugely popular free messaging app that was created way back in 2009.

Facebook bought out the service for an incredible $19.3billion in February 2014 – one of the largest tech acquisitions in history.

A big perk of WhatsApp is its end-to-end encryption feature, which protects the contents of users' messages from outsiders.

It works by encoding messages so that only the sender and receiver can read them, blocking out everyone else – including WhatsApp itself.

WhatsApp is available on Google's Android, Apple's iOS. Microsoft's Windows Phone, BlackBerry OS, Symbian, and in web browsers through WhatsApp Web.

We've asked WhatsApp for comment on this story, and will update our article with any response.