Rescuers have found the body of missing hiker Lily Hooper in a tragic end to the lengthy search in the NSW Southern Highlands.

Authorities found the body, which has not yet been formally identified but is believed to be Hooper, in bushland about 11.30am on Thursday.

But in a devastating bungle, she was publicly declared alive and her family believed this to be true for “eight to 10 minutes”.

Her parents expressed relief to the media before being told their daughter may not be alive.

NSW Premier Chris Minns initially shared the “fantastic news” that the 18-year-old had been discovered after more than a week.

“(Lily Hooper was) found in the bush with half a bottle of water with her,” he said.

“I just want to thank the NSW Police, the SES, the Australian Defence Force, and literally the hundreds of volunteers who got in there and helped.”

However, he later confirmed the sad reality that the Oakdale teen was dead.

“I’ve got some terrible news…but it seems as if the early advice was wrong,” he said during budget estimates.

“Lily’s body has been found, and she has been found deceased. I only raise that because I made the earlier advice and I’m very sorry for that.

“This is obviously devastating and I’m just profoundly sad for her family and all those concerned.

At a press conference later, NSW Assistant Police Commissioner Joseph Cassar faced intense questioning, but insisted that police had not “jumped the gun”.

An SES volunteer found her about 11.30am on Thursday, but a communication breakdown led to incorrect reporting to her family, Cassar said.

“(The family) were informed (of) initial information the searchers believed she was alive, and that’s what was communicated,” Cassar told reporters.

“Within eight-to-10 minutes we were able to give them an update which was a more accurate account.”

The senior officer apologised to Hooper’s family for the miscommunication and the loss of their beloved daughter.

“Every one of the investigators and the searchers, whether they were volunteers or paid personnel, hoped for a more positive outcome,” Cassar said.

“If we were able to provide them more detailed information on that first report, I can tell you that would have been the case.”

Cassar said the chain of communication between authorities and the family would form part of the investigation for the coroner.

Cassar said he was not aware who informed the premier of the incorrect details of the discovery.

Cassar said the discovery of Hooper’s body, which was a “significant distance” from her car in bushland that was “very very difficult to navigate”, was a tragic end.

“It is certainly not the outcome that we hoped and there is great sadness out there with all the searchers involved,” he said.

Her body was not on located a clear walkable track but in “thick, dense bush” in a “steep cliff area,”said Cassar. 

Hooper had been missing since last Wednesday, August 12, after embarking on a hike in the Nattai National Park in NSW’s Southern Highlands.

The Oakdale teen did not return that evening and could not be contacted on her mobile phone, triggering a wide-scale search.

Hundreds of emergency personnel, loved ones and volunteers battled unforgiving conditions across the weekend to no avail.

Detective Inspector Brendan Bernie said Hooper was an experienced bushwalker and they hoped that would get her through the ordeal.

But for more than a week searchers found no trace since they discovered her car at the Bonnum Pic trailhead last Wednesday night.

On Tuesday, Hooper’s family said they were “absolutely devastated that our beloved daughter Lily is missing”.

“We desperately want to bring Lily home safe and we ask as the search continues, to keep our family and Lily in your thoughts.”

The family thanked the emergency services and volunteers for their support and commitment to the search — “not only during the day but throughout the night”.

“We appreciate people who have made offers for the search but, due to the terrain and conditions, we ask just professional search teams continue,” they said.

“We also ask for privacy and understanding as our family navigates this unimaginable situation.”

The search included crews from NSW Police, the Rural Fire Service and the State Emergency Service.

Rescuers met with rugged, dense terrain at the national park and cold, wet and foggy weather.

Police also used a thermal imaging helicopter at night.

-with AAP