Two people have died and two others are in a critical condition after a landslip in NSW's Blue Mountains on Monday.
NSW Police said a 49-year-old man and a nine-year-old boy have died while a woman and a second boy are in a critical condition after being treated at the scene on Wentworth Pass in Wentworth Falls.
Acting Superintendent John Nelson said the group were bushwalking when they were crushed by falling rocks in a landslip.
"There were five people that were bushwalking, unfortunately there has been a landslip while they have been bushwalking," he said.
"As a result of that there has been a police operation that is in process as we speak. That is a rescue and recovery operation.
"Unfortunately, as part of that landslide there has been a man and a boy who have passed away."
Police confirmed the family were British nationals on holidays from the United Kingdom, and the British Consulate was assisting.
The bodies of a man and young boy remain at the popular walking track, while a 50-year-old woman and a 14-year-old boy are in a critical condition at Westmead Hospital and Westmead Children's Hospital after being rescued by helicopter.
Emergency services will launch a recovery mission to retrieve the bodies later this morning.
Acting Superintendent Nelson said a 15-year-old girl was walked out of dense bushland by paramedics, and she is lucky to be alive.
"It's quite a tragic scene, we do have a girl who is walking out at the moment who is obviously extremely distressed and we're trying to talk to her to obtain further information," he said.
NSW Ambulance Acting Chief Superintendent Stewart Clarke said the incident had been "a heartbreaking experience" for everyone concerned, and ambulance chaplains and peer support were available to assist.
"Any situation as has been described is obviously exceptionally confronting and heartbreaking, especially when you start involving children," he said.
He said the woman and boy had been treated by paramedics at the site of the landslip after suffering significant head and abdominal injuries.
The pair was sedated and intubated for their injuries before being moved, he said.
Mr Clarke said it's believed someone in the group or someone nearby called Triple 0 to provide the location.
He described the rescue operation by paramedics as conducted under extreme conditions in an extremely unstable environment.
Paramedics had to be winched down to the site in dense bushland.
The popular hike is now under police guard and questions are being asked about why it was open given the recent deluge.
