WhatsApp has gone down for users across the UK, with tens of thousands of people reporting being unable to send or receive messages.
Downdetector, which tracks outages, said more than 57,600 reports of problems had been submitted at 8.41am, with issues first detected just before 8am.
However, the number of users experiencing issues could be much higher due to the way the website collects data.
WhatsApp users from around the world have taken to social media platforms, such as Twitter, to complain that the app is not working.
Downdetector also found more than 11,000 users in India, and 19,000 in Singapore, had reported experiencing issues.
Users have found that while they can open the app and access their conversations, it is failing to deliver new messages or successfully send any.
A persistent message is showing for many users at the top of the app, saying it is “connecting” to the server, but then appears to fail to do so.
“We’re aware that some people are currently having trouble sending messages, and we’re working to restore WhatsApp for everyone as quickly as possible,” a spokesperson for the platform’s parent company, Meta, said.
Some of the most concerned users are likely to be Conservative MPs, with the platform widely used by backbenchers, Cabinet ministers and aides to discuss public messaging.
A Cabinet reshuffle will be taking place today, so many MPs hopeful of landing a ministerial job will currently be without a vital way of sounding out advisers on their chances of being appointed.
The app has previously been identified as a tool of choice for MPs plotting against their leader, and Boris Johnson is said to have often been sent summaries of key government information via the platform while he was prime minister.
WhatsApp is one of the most popular messaging platforms in the UK and around the world, and is estimated to have more than two billion active users globally.
