Google has launched a new tool that allows mobile phone users to track friends and contacts on its Google Maps software.

The new feature, called Latitude, will allow users to share their location with other mobile phone users and find contacts who are located nearby.

As part of the Google Maps 3.0 software, Latitude will initially only be available on BlackBerry mobile phones and devices with Windows Mobile and Symbian S60 operating systems.

In coming weeks, users of the iPhone and Google Android phone will also be able to use the software. Senior executives at Google said that Latitude was designed to answer the question that almost all mobile phone users ask first when making a call: "Where are you?"

The new software will answer that question on-screen by leaning on local wi-fi services and phone masts to triangulate a fellow user's approximate position. Not so useful when one needs to make excuses for being late.

"We believe this is the kind of technology that will allow people to meet up more spontaneously with those they happen to be around," said Hugo Barra, group product manager at Google Mobile. "It's a very intuitive service."

The software will be an opt-in service, so a user's consent to having their location revealed is not presumed.

They can also choose to go temporarily "off-grid", and control how much detail they reveal about their location, for example limiting information about their whereabouts to the name of the city they are in. Mr Barra said: "Privacy is one of the areas we spent the most time perfecting."