A device attached to a terrified Sydney teenager for 10 hours on Wednesday was a fake, police have confirmed on Thursday.

"A very, very elaborate hoax as it turned out," New South Wales (NSW) Police Assistant Commissioner Mark Murdoch said on Thursday after police released 18-year-old Madeline Pulver from the device following a delicate 10-hour operation.

"But it was made and certainly gave the appearance of a legitimate improvised explosive device. We had to treat it seriously until we could prove otherwise and that's exactly what we did and that's why it took so long." Murdoch told reporters in Sydney.

Murdoch said the 10-hour operation involved a large number of police from many specialist units and agencies.

NSW police also sought advice from British military experts and the Australian Federal Police as they worked to make the device safe.

The young woman was taken to the Royal North Shore Hospital for checks and was released on Thursday morning.

The suspected bomb was reportedly attached to the young woman after a masked man burst into her family home about 2 p.m. (local time) on Wednesday.

The drama began when the 18-year-old girl called police to her Mosman home about 2:30 p.m. (local time) on Wednesday.

Murdoch told reporters outside Madeleine's home it was "far too early" to establish a motive for the attack.

He declined to detail any demands made by the person who has so far evaded police.

"Certainly the family are at a loss to explain this, but you wouldn't expect someone would go to this much trouble if there wasn't a motive behind it," Murdoch said.

"What this motive is, we are still not aware."

Police form strike force to investigate Sydney bomb hoax

A police strike force has been formed to conduct inquires after a Sydney schoolgirl was targeted in an elaborate bomb hoax, New South Wales Police said on Thursday.

Robbery and Serious Crime Squad Commander, Detective Superintendent Luke Moore, said police were treating the incident as an attempted extortion.

"We have established Strike Force Haddon to examine this incident and the motivation behind it," Moore said.

"We are pursuing a number of lines of inquiry. However, it appears at this stage to be a case of attempted extortion," he said.

Local police officers attended a residence in Burrawong Avenue at Mosman, on Sydney's lower north shore on Wednesday afternoon, after receiving reports of an 18-year-old woman required urgent police assistance.

Arriving on the scene, police found the girl was in distress with a suspicious device fitted to her neck by a chain.

After an extremely delicate and tense operation lasting about 10 hours, the girl was freed from the device in the early morning on Thursday.

Police have been told an unknown balaclava-clad man confronted the victim in the kitchen and forced her to stay still while he fitted the device to her on Wednesday afternoon.

The girl's father on Thursday told reporters in Sydney that his daughter was coping well from the horrifying ordeal though she was tired and sore.

"From our family's perspective we are clearly extremely eager for our lives to return to normal," he said.

"Our appeal to you is that you request our privacy after this and leave us to get on with our lives," he added.

VietNamNet/Xinhuanet