SAN FRANCISCO (AFP) - Facebook-owned smartphone messaging service WhatsApp has hit the billion-user mark, according to the leading social network's chief and co-founder Mark Zuckerberg.

"One billion people now use WhatsApp," Mr Zuckerberg said in a post on his Facebook page.

"There are only a few services that connect more than a billion people."

Google's free e-mail service, Gmail, is the latest of the Internet giant's offerings to crest the billion-user mark, chief Sundar Pichai said on Monday (Feb 1) during an earnings call.

The WhatsApp team said in a blog post: "That's nearly one in seven people on Earth who use WhatsApp each month to stay in touch with their loved ones, their friends and their family."

The ranks of people using WhatsApp have more than doubled since Facebook bought the service for US$19 billion (S$27 billion) in late 2014, according to Mr Zuckerberg.

After buying WhatsApp, Facebook made the service completely free. The next step, according to Mr Zuckerberg, is to make it easier to use the service to communicate with businesses.

Weaving WhatsApp into exchanges between businesses and customers has the potential to create revenue opportunity for Facebook.

Recent media reports have indicated that Facebook is working behind the scenes to integrate WhatsApp more snugly into the world's leading social network by providing the ability to share information between the services.