YouTube has stopped working for some of its users, leaving them unable to watch videos.
Affected people instead saw a monkey dressed as a builder alongside an error message.
"Sorry, something went wrong," it said. "Try reloading the page. We're working hard to fix YouTube for you as soon as possible."
Despite the error message, reloading the page did not cause videos to load.
But the issues did not appear to be affecting every user. Despite vast numbers of reports of problems, some were able to watch videos as normal.
Others said the problems only appear on particular parts of the site, such as channel pages.
The issues appeared to be focused on the west coast of the US as well as some parts of Europe, according to tracking website Down Detector.
YouTube, which is owned by Google and powered by its technology, rarely goes offline. But even a short or patchy outage can cause vast problems, since so many people use it.
YouTube says that more than a billion hours of video are watched on its platform each day, and nearly two billion logged in users visit it each month. It is available in just about every country in the world, with 91 different localised versions available.
