Google's YouTube said 1 billion unique users were now visiting the video-sharing website every month, or nearly one out of every two people on the Internet.

"If YouTube were a country, we'd be the third largest in the world after China and India," YouTube said in a blog post on Wednesday.

Expanding high-speed data networks across the world and increased availability of internet-enabled smartphones have helped to connect billions of people to the Internet, fuelling growth in social media and video-sharing websites.

Facebook reached 1 billion active users in September, a level of global penetration that has made its quest for sustained growth more challenging.

Both YouTube and Facebook took eight years to cross the billion-user threshold.

YouTube was an instant success after its founding by three former PayPal employees in 2005, adding millions users in its first year. Google bought it for $1.65 billion in 2006.

The video site now represents one of Google's key opportunities to generate new sources of revenue outside of its traditional internet search advertising business.

The popularity of music videos such as South Korean singer Psy's "Gangnam Style" has contributed to an explosion in viewership on YouTube. The video has so far clocked 1.45 billion views. – Reuters