The website and app appear to be down and are failing to load.
Users report seeing a strange "error 404" instead of their messages.
"404. That's an error," the message reads, alongside a picture of a broken robot. "The requested URL was not found on this server. That's all we know."
Problems were hitting users all over the world, according to the site Down Detector. While they were particularly focused in western Europe, that is likely to be a result of timezones meaning most users are online there.
Google said it was aware of the problem and would be posting updates as it attempted to fix it. The next update is due around 1pm UK time, it said.
"We're aware of a problem with Gmail affecting a significant subset of users," the Gmail status page read. "The affected users are unable to access Gmail.
"We will provide an update by 1/29/19, 12:50 PM detailing when we expect to resolve the problem. Please note that this resolution time is an estimate and may change."
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