WhatsApp appears to have stopped working, with users unable to send some messages.
While text appears to work, photos, videos and voice messages will not send through, according to various reports.
Instead, users just see a message reading "download failed" and the content will not arrive.
The same error message advises users to ask for the picture to be sent over again. But doing so does not seem to work.
Unusually, a preview of the picture does appear to be able to get through. It means that recipients can see a version of the pictures that are being sent – but it is fuzzy and the details cannot be seen.
Sometimes, an error message will show confirming that something has gone wrong, though it does not appear to show up every time.
The wording of the error messages appears to change for different users. But many of them suggest solutions that don't actually seem to work.
"Couldn't download image," one seen by The Independent reads.
"Try again. If the problem keeps happening, try turning off Wi-Fi or VPN, or connecting to a different Wi-Fi network."
Complaints particularly came from the UK and South America, according to the outage tracking website Down Detector. The number of reports were relatively limited for a WhatsApp outage – but that might be a consequence of the strangely specific nature of the problem.
Unlike many other major services, WhatsApp does not maintain a status page to allow people to check whether its systems are online. It does have a Twitter account that was once used to alert people to issues, but it has not been used for five years.
Last time all three of Facebook's major services broke, the outage lasted for many hours. It later blamed that problem on a server issue that had a knock-on effect on Instagram and WhatsApp, as well as Facebook, since the three use shared infrastructure.
"As a result of a server configuration change, many people had trouble accessing our apps and services," Facebook posted on Twitter after that previous outage was fixed. "We've now resolved the issues and our systems are recovering. We’re very sorry for the inconvenience and appreciate everyone’s patience."
When those problems happened in March, they were said to be perhaps the biggest outage in the history of the internet, hitting millions of people.
“By duration, this is by far the largest outage we have seen since the launch of Downdetector in 2012,” Tom Sanders, co-founder of Downdetector, told Techcrunch in the wake of that outage. “Our systems processed about 7.5 million problem reports from end users over the course of this incident. Never before have we such a large scale outage.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies