A rockfall that killed a worker and trapped two others in the Blue Mountains National Park sounded like dynamite going off, says a bushwalker who subsequently heard terrible screams.
Mike Burgess was walking near Wentworth Falls when a section of sandstone cliff fell nearby killing a 36-year-old contractor and trapping two others.
"A big explosion of rocks must have fallen ... I think the workers were working on the National Pass above me," he told the ABC on Wednesday.
"It sounded like dynamite, but I knew it wouldn't be dynamite, it would be a big slab (of rock)."
Mr Burgess said the explosion was followed by screaming.
"I heard the screaming and that so (expected) some pretty bad injuries," he said.
The three contractors were working on the historic National Pass track - parts of which were built by hand in the early 1900s - when the rockfall occurred just before midday on Wednesday.
The track was closed in late August "due to a very dangerous, unstable section of rock above the walking track", the National Parks and Wildlife Service said at the time.
The area was assessed by geotechnical engineers with work being conducted to remove the "extreme hazard".
The two other workers - aged 26 and 27 - were winched from the scene on Wednesday afternoon and flown by helicopter to Westmead Hospital.
