NSW Police and Ambulance NSW confirmed two people died and two were critically injured after a rockfall at Wentworth Falls shortly after 1.30pm on Monday.

The walking party was a family of five - a man, 49, and a nine-year-old-boy, have died - while a woman and a boy were in a critical condition and receiving medical care on site.

NSW National Parks and Wildlife Service (NPWS) spokesperson said the walking track was inspected in the days before the rockslide as part of a routine track assessment program.

"NPWS has a world class program in place to assess geotechnical risks and maintain the safety of walking tracks and other infrastructure to the greatest extent practicable. Unfortunately it is not possible to predict and eliminate all natural risks such as rockslides, which can occasionally occur around the state," the spokesperson said.

The woman, 50, and second boy, aged 14, were winched from the location just before 6pm on Monday and taken to Westmead Hospital and the Children's Hospital at Westmead, both in critical conditions.

A 15-year-old girl was walked out by emergency services and treated by NSW Ambulance paramedics for shock and taken to the Children's Hospital at Westmead.

The five people are all members of the same family and are British nationals who were holidaying in Australia, police said at 10pm on Monday. The British Consulate is assisting in the matter.

NSW Ambulance Acting Chief Superintendent Stewart Clarke said it was "absolutely heartbreaking for all involved and a truly tragic ending to what I'm sure was meant to be a pleasant day out".

"It is terribly sad to have lost two lives here today and my heart goes out to the families and the survivors of this horrific ordeal who have witnessed what is certainly a traumatic event.

"This was a really complex and delicate rescue operation for our crews who were working to access patients in rugged bushland and were navigating unstable ground."

Supt Clarke said the patients being winched out of the site had significant head injuries and would require sedation and intubation.

Seven paramedic road crews including special operations paramedics and two rescue helicopters with a critical care doctor and a critical care paramedic on board were dispatched to the scene shortly after 1.40pm. On arrival, paramedics located five people; two with critical injuries, one was uninjured and two died at the scene.

Ambulance chaplains are on site to help with the tragedy.

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The rescue took place in the area of the popular Wentworth Pass Loop walking track, a five kilometre walk which is described as challenging.

Blue Mountains Area Commander Detective Superintendent John Nelson said it was a very tragic scene.

"The girl is extremely distressed and we are trying to talk to her," Supt Nelson said.

"Our rescuers are working under quite arduous conditions." The area was still unstable and rescuers were working in an unsafe environment.

A NSW Police Media spokeswoman said "about 1.40pm today (Monday April 4) emergency services were called to Wentworth Pass, Wentworth Falls, due to concerns for the welfare of five bushwalkers following a landslip near the pass". The landslip happened from above.

A Blue Mountains Gazette reporter at the scene said there were about 50 emergency services vehicles there, including from the NSW Ambulance, Police Rescue, Fire and Rescue NSW, Police as well as National Parks and Wildlife staff.

State Emergency Services volunteers arrived on the scene in the afternoon and joined National Parks climbers and Police Rescue specialists who were taken into a briefing.

Ominously just last week National Parks and Wildlife Service Upper Mountains area manager Will Batson expressed concerns to the Blue Mountains Gazette about track safety after heavy rainfall.

Mr Batson said Parks was looking into the permanent closure of at least one track further up the Mountains in Blackheath because of concerns for safety due to damage from landslides following fires and floods.

He told the Gazette in relation to Rodriguez Pass that "NPWS takes the risk of landslides and rockfall seriously, in accordance with a policy developed following the accident on National Pass in 2017 where a contractor died, and another two were significantly injured".

He said NPWS "considers worker and visitor safety as an absolute priority when evaluating these risks" and that the coming weather window did worry him.

"We are heading into the unknown. If the wind really picked up the soil is saturated the trees will fall over and that is often the trigger for a landslide," he told the Gazette.