Sydney (CNN) -- Bomb-squad officers in Australia have freed an 18-year-old girl who was inside a house in Sydney with a suspicious device, police said Thursday.
Assistant Commissioner Mark Murdoch said the girl had been released and was safely back with her family.
He said she had been in an extremely uncomfortable position for many hours and would be taken to hospital as a precaution.
The police would closely examine the scene and the device itself, which was "very elaborate and sophisticated," he said in a prepared statement.
The situation, in the wealthy suburb of Mosman, was resolved soon after midnight Thursday, after what New South Wales police said was a 10-hour operation.
"The safety of the young lady was always our first priority, and I am pleased to say we have achieved this," Murdoch said. "Her parents, in particular, are extremely relieved.
"This outcome is a testament to the skills of NSW Police bomb technicians, who have worked tirelessly in very difficult conditions," he said.
Officers had been contact with explosives experts in Europe and the United Kingdom during the operation, Murdoch added.
The alarm was first raised at about 2:30 p.m. Wednesday, police said.
The force has not confirmed reports that the device was some kind of collar bomb, but speaking at a news conference before the teenager was freed, Murdoch said the "life of a young lady is potentially at risk."
The police are treating the incident "very, very seriously," he said.
"There is a device that we are examining and it's proving a tough nut to crack for us to determine what it is and what it is not," Murdoch said, describing the operation as "painstaking and very intricate."
Nearby homes were evacuated and neighboring streets closed off by police. Footage from the scene showed numerous emergency response personnel and vehicles stationed along the street.
Australian news reporter and Mosman resident Dave Kirwan told CNN late Wednesday that the police had not given much detail but had said the girl was not able to leave the vicinity of the device, suggesting she could be attached to it.
Kirwan said he had caught a glimpse of the girl's parents outside the property, looking distraught.
Police told reporters there were four people inside with the girl and they were trying to keep her calm, he said.
About eight hours into the situation, some people living in the immediate vicinity were told they would not be able to go home for the night, he said.
Mosman is a very wealthy suburb on Sydney Harbor, where many well-connected people, sports stars and celebrities live, Kirwan added.
"This kind of thing doesn't really happen here," he said. "Everyone is really, really scared."
Many residents had locked themselves into their homes when the alarm was first raised, he said, fearing that they might also be in danger.
In a statement on the New South Wales police website earlier Wednesday, Murdoch said the incident was highly sensitive.
"While the very delicate operation continues at the house with the bomb squad officers, highly skilled investigators have been working behind the scenes since the incident was first reported," he said.
"Given the nature of the incident, I am sure you can all appreciate we need to keep the cards very close to our chest."