The Independent reports that the WhatsApp app doesn't initially look broken, with chats and contacts able to load. But once a user is into a chat, the app just shows a "connecting" message that never resolves itself, and so new messages can't be sent or received.

That also means there's no easy fix to the problem, since it appears to be on WhatsApp's side. Shutting and opening the app, for instance, just resets the connecting message but won't stop it showing.