The Robinson R44 light helicopter clipped a tree just after midday, crashing into a grassy area near the restaurant before bursting into flames and killing everyone aboard.

It was initially believed that the passengers, who left from Bankstown Airport, were part of a wedding party and a child was on board.

Photos of rescue and forensic workers at Bulli Tops

It was later confirmed the four dead were adults, but police last night had not released details of the sex, age or relationships between the passengers.

When the first rescue workers arrived at the scene, they witnessed restaurant staff trying to fight a ‘‘significant and volatile’’ blaze with fire extinguishers, Fire and Rescue NSW Superintendent Steven Baker said.

‘‘Local workers had attempted to extinguish the fire and [the fire crews] then proceeded to extinguish the fire with foam,’’ he said.

Mr Baker commended the Panorama House staff for their bravery.

‘‘I think it’s a very brave action that they have put their own lives at risk in an attempt to save others,’’ he said.

‘‘It’s generally acknowledged that aviation fuel is highly volatile.’’

Bulli resident Norm Upton was driving home from Sydney south along Mount Ousley when he saw ‘‘a black ball of smoke’’ and the helicopter engulfed in flames.

‘‘I was about 200 yards away and I saw people running around,’’ he said.

‘‘There was dust and dirt and that all around the place and the ball of smoke was about 100 metres up in the air.’’

Another witness, who was working in nearby bush at the time of the accident, said he heard a huge crash and saw the burning wreckage of the helicopter about five minutes later.

A group of elderly people from the St George area were inside the venue, along with staff, who appeared distraught as they avoided the media while leaving the area.

Wollongong Detective Inspector Tim Beattie said it was too early to identify the passengers or explain how the crash had happened.

He said it was highly likely the crash victims were planning to have a meal at Panorama House.

‘‘As you can imagine, it’s a horrific scene for all involved and it will take some time to examine and recreate the scene and determine who was on board,’’ he said.

‘‘Our first priority is to get the correct information to the families.’’

Inspector Beattie said police had invested ‘‘significant resources’’ in examining the crash site but expected it to take days, and potentially months, for the full details to surface.

‘‘We are in the process of interviewing a number of people, including the workers who responded to the fire,’’ he said.

‘‘A number of people have already been spoken to, but I would appeal to anyone who hasn’t been spoken to or particularly anyone who has recorded any image of this incident to please make yourself known to Crime Stoppers or Wollongong police.’’

He said counselling was being offered to staff and customers of Panorama House who were ‘‘shaken’’ by the incident, as well as emergency services crews who were first on the scene.

On Thursday night, a police media spokesman said disaster experts were wrapping up their investigations of the crash site, with the remains of the bodies expected to be removed and taken to Glebe morgue overnight.

Police expect to hand over their crime scene to aviation investigators some time on Friday.