Disruptions in the service have been reported since 11:26 GMT. Most of the complaints are related to the website’s operation or watching videos.
YouTube is down for thousands of users across the globe, according to DownDetector, a service registering distruptions on popular websites.
In the UK, a maximum of 7,513 crash reports were submitted to the site, while in the United States, the figure reached 21,849.
Both countries reported problems watching videos and using the site, while a smaller portion of users had problems logging in.
The video service has so far provided no explanation as to what caused the malfunction.