The sites displayed error messages, leaving users unable to access them.
DownDetector, a website that detects whether sites are down, says that the issues started at around 11:56 GMT.
The site recorded more than 43,000 reports of YouTube being down.
The technology giant's service status website confirmed the firm's entire suite of apps had suffered an outage, but did not confirm what had caused the issue.
It added that it was "aware of the problem" and that it had left the "majority" of users unable to access its services.
Google later said it had restored service for the vast majority of its users, just over an hour after the outage was first reported.
The company said it would “continue to work towards restoring service for the remaining affected users” but that no further updates would be provided via its service status website.
“Please rest assured that system reliability is a top priority at Google and we are making continuous improvements to make our systems better,” the company said.
Some of Google's services are among the most widely used in the world - YouTube has more than two billion active users, while Gmail is the world's most popular email platform with other 1.5 billion users.
Many took to social media to share their frustration with the outage, with the technology giant quickly trending on Twitter.
