'After that I heard screaming': One dead, two injured in Blue Mountains rockslide

A massive rockfall on a Blue Mountains walking track has killed a 36-year-old man and seriously injured his two workmates.

Helicopter crews have since rescued the survivors from a cliff face at Wentworth Falls.

The trail they were on was closed months ago due to the danger posed by a rockslide.

Ironically, the three men had been sent in to make the track safe.

The walk, known as the National Pass, is considered one of Australia's best bushwalking tracks.

But it's also dangerous, with its Grade 4 listing in the in the Australian Walking Track Grading System meaning that bushwalking experience is advised due to the long, rough and steep tracks.

On Wednesday part of a sandstone cliff on the Pass sheared away, crushing the three National Parks and Wildlife Service contractors who were endeavouring to stabilise the area for the 90,000 people who walk the track every year.

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"We all heard the rocks smash down through the bush and then straight after that I heard all the screaming, so some pretty bad injuries down there, I'd say," bushwalker Mike Burgess said.

Blue Mountains Police Supt Daryl Jobson said: "Obviously this is a tragic incident and a sensitive operation."

It was difficult to reach the site, an hour's walk into the bush, and too far for the three men to be carried out.

Instead, winches were required.

Two paramedics accessed the men, then two medical teams were winched in.

Emergency services worked as swiftly as they could, not just for the welfare of the survivors but for their own safety.

With rain in the area, there is also the potential for further landslides.

Authorities have described it as a "routine" job, surveying the rocks and trying to make the tracks safe.

But the track has been closed since August with the following message: "The area has been assessed by a geo-technical engineer and appropriate measures will be implemented to remove this extreme hazard."

Distressed relatives of the injured survivors, who are 26 and 27 years old, were escorted to the scene.

The 27-year-old has sustained leg and pelvic injuries and both survivors were airlifted to Westmead Hospital.

Relatives of the 36-year-old deceased man were notified on Wednesday evening but the man's body remains at the site, with police deeming the area a crime scene.

Assessors are expected to return to the area on Thursday morning to ascertain the safest way to remove the man's body.

According to National Parks and Wildlife data, there have been six deaths in the Blue Mountains National Park since 2000.

- With AAP