An 18-year-old Sydney schoolgirl is caught in a horrifying bomb scare tonight after a balaclava-clad man entered a Mosman house and reportedly attached a device to her this afternoon.



Police said they were treating the device as live until they knew otherwise.

“It’s a very serious incident where the life of a young lady is potentially at risk and we’re dealing with it in that light," assistant commisioner Mark Murdoch told media at the scene.

Police and bomb squad at the Mosman house. Credit:Brendan Esposito

He said the teenager, who was alone in the house at the time of the attack, was doing a "great job" keeping her emotions in check.

The girl's parents are outside of the house in Burrawong Avenue and have not been allowed to speak to their daughter.