FACEBOOK has stolen a march on rivals by announcing plans for its own internet search engine, raising questions about the privacy of its one billion users.

The social networking website's founder and chief executive Mark Zuckerberg unveiled the service, Graph Search, which puts his company into direct competion with Google.

He stressed the product was "very, very different" to web search engines offered by other tech giants such as Google because it only looks for data on Facebook itself.

It will allow users to search for people, photos, places and other content shared on the network.

The announcement came after fevered specula- tion over what would be unveiled at Mr Zuckerberg's presentation. He said the new search tool would be rolled out "very slowly", starting with a beta version available to limited users.

"This is one of the coolest things we have done in a while," he said, adding: "Graph Search is the kind of product we love to build at Facebook – it's a big technology problem and it's also a big social problem."

Facebook said an opt-out would keep user's content out of searches. But Chris Edwards, an electronics correspondent for Engineering and Technology magazine, said: "People don't really think about privacy. But if you look at some of the features on Facebook, it's almost like a stalker's tool kit."