WhatsApp wasn't working for many user across the world this morning.
Outages have been reported in the UK, Myanmar, Russia, Vietnam and Brazil.
The service began to function again about 30 minutes after the initial complaints, according to Reuters, although there are still some reports of issues on social media. It is not known why the outage occurred.
WhatsApp, owned by Facebook, is one of the world's most popular messaging apps with one billion daily active users.
Facebook bought WhatsApp in 2014 for a staggering $19 billion.
The company did not immediately respond to a request for comment.