Video sharing site YouTube has announced that it has passed one billion regular monthly users.

YouTube, which is owned by Google, announced the milestone on its blog.  It said a recent increase in smart phones had boosted numbers visiting the site each month.

YouTube was started in 2005 and was purchased by Google in 2006.  At the time it bought the site: for $1.76bn (£1.16bn), it had an estimated 30-40 million users worldwide.

With one billion users monthly, YouTube poses a challenge to Facebook as the largest social network on the Internet.  Facebook celebrated a billion users in October last year.

“Nearly one out of every two people on the Internet visits YouTube,” a statement from the company said.

“Tens of thousands of partners have created channels that have found and built businesses for passionate, engaged audiences. Advertisers have taken notice,” it said, commenting that the top 100 brands shown by trade magazine Advertising Age had running campaigns on YouTube.

The YouTube site was launched by three former PayPal employees in California.

The first video that was uploaded to YouTube was by co-founder Jawed Karim and called Me at the Zoo.