Popular messaging service WhatsApp last evening experienced a major outage. According to a variety of reports on social media, users were unable to access the service and could not send or receive any messages.

On attempts to access the web interface of WhatsApp, for instance, you would receive a “Trying to reach phone” message, but never actually get connected.

WhatsApp acknowledged the outage in a statement to media outlets, saying it was aware of the issues and working on a fix. At that point, however, it was unclear what the actual issue was nor when a fix would be deployed.

Although many users appear to be back to normal there’s still hundreds of WhatsApp users who still can’t access the app across the UK and Brazil, according to reports.

The company hasn’t yet communicated the reason for the outage.

WhatsApp is used by more than 1.2 billion people around the world and is a key tool for communications and commerce in many countries.