BRUSSELS: The European Commission launched an "in-depth investigation" on Tuesday into whether US tech giant Google's planned $2.1 billion purchase of smartwatch maker Fitbit would give it an unfair market advantage.

"Our investigation aims to ensure that control by Google over data collected through wearable devices as a result of the transaction does not distort competition," EU competition commissioner Margrethe Vestager said.

In November last year Google announced it had reached agreement to buy Fitbit, which produces wearable fitness trackers and watches that communicate with a health monitoring app.

But Google also produces an operating system for smartwatches and Brussels is concerned that acquiring Fitbit's user data will strengthen its already powerful position in targeted advertising.

"The use of wearable devices by European consumers is expected to grow significantly in the coming years," Vestager said in a European Commission statement announcing the probe. "This will go hand in hand with an exponential growth of data generated through these devices. This data provides key insights about the life and the health situation of the users of these devices."

Google has promised not to use Fitbit health and wellness data for Google ads, but the buy out has attracted concerns from consumer groups and Australia's competition commission.

The European Commission now has 90 working days - or until December 9 - to carry out the investigation and decide whether to impose new conditions on Google.