Users of WhatsApp were struggling to send texts after the web-based messaging service went down.
Users of the service from around the world reported difficulties with outages on Thursday (30 November) affecting people in Europe, the Middle East, Africa, Asia and the US, the website DownDetector said.
The website showed that there were peak outages at around 6pm GMT, with messages not being sent of received, spurring users to take to Twitter to complain.
WhatsApp is the world's biggest messaging service with 600 million users and has been owned by Facebook since 2014.
Normally reliable, it has crashed before, back in May and also on New Year's Eve last year. WhatsApp is yet to address the issue on its communications platforms.
A spokesperson for Whatsapp said: "WhatsApp users around the world are unable to access the service. We apologise for the inconvenience and are working to fix the issue as soon as possible."
Last month, Whatsapp unveiled a feature allowing users to "unsend" embarrassing messages on the latest versions of iPhone, Android, Windows Phone as well as desktop.
"Starting today you can now delete messages you sent by mistake — whether to one person or an entire group," Whatsapp said in a blog post.
"Here's how it works: tap and hold on the message, choose 'Delete', and then 'Delete for everyone'. You have seven minutes to delete the message after it's sent.