WhatsApp, the messaging platform, has gone down across UK and the rest of the world.
It is not known what is causing the issue.
WhatsApp is owned by Meta, the global tech giant formerly known as Facebook (FB) and has two billion worldwide users.
Tens of thousands of UK users have taken to social media, complaining they are unable to send or receive messages on the popular Meta-owned service.
According to reports, WhatsApp has confirmed it is aware of the issue and is working to fix the problem.
After opening the app this morning, users found they can still access their conversations but the app is failing to deliver new messages or send any that they attempt to transmit.
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, leaving users unable to send or receive any messages.
According to the service status website Downdetector, users began reporting issues with WhatsApp at just before 8am on Tuesday morning, with more than 12,000 reports of issues reported to the website by 8.30am.
WhatsApp is one of the most popular messaging platforms and is estimated to have more than two billion active users globally.
In a statement, a WhatsApp spokesman said: “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.”