Sydney teen in bomb emergency

An 18-year-old woman remains near a suspicious package inside a house on Sydney's lower north shore, police say.

Bomb technicians and negotiators are with the teenager in the house as a major operation involving the bomb squad, rescue squad and police continues at Mosman, Assistant Commissioner Mark Murdoch told reporters on Wednesday.

Police found the teenager alone in the house on Burrawong Avenue after emergency services were called at 2.30pm (4.30pm NZT) on Wednesday.

Mr Murdoch would not confirm reports the bomb is attached to the young woman, but said she remained in the house near the device.

"There's a device in the house in the vicinity of the young woman. That device is still being examined as we speak," Mr Murdoch said.

"We are treating the device as live until we know otherwise."

There are reports the device was attached to the woman by someone she didn't know.

Mr Murdoch described the incident as "very sensitive".

"We need to play our cards pretty close to our chest at this point," he said.

"The young lady is fine and doing her best to assist the police to find out exactly what's gone on," he said.

Police said in a statement the incident was not being treated as self-harm.

Nearby homes on the street, where multi-million dollar properties include one belonging to horse trainer Gai Waterhouse, have been evacuated and nearby streets have been closed off.

The rescue squad are also at the house, and fire crews and paramedics are on standby.

A middle-aged man and a woman were seen with police officers outside the house, with the woman wiping away tears.

- AAP