Fourteen people plunged 30 metres to their deaths late yesterday morning when a viewing platform on a track in the West Coast's Paparoa National Park collapsed.
Thirteen of the dead were students on a one-day geology field trip from Tai Poutaini Polytechnic in Greymouth. The other was a Department of Conservation staff member accompanying the party.
Four people who survived the terrifying plunge were in hospital last night, three of them in a serious condition.
The 18 people were on the platform above a large subterranean hole in limestone at Cave Creek when the structure gave way. All were thrown into the chasm.
Five of the 13 students who died were women.
The four survivors were in hospital last night, three in a serious condition. One has been flown to Christchurch for intensive treatment.
Grey Hospital manager David Meates would not give details of their condition.
All the students were taking a one-year outdoor education course.
A police statement last night said 20 students and one tutor were on the trip to the park about 45km north of Greymouth. After a briefing at park headquarters at Punakaiki, a popular coastal tourist spot, the party was driven several kilometres along Bullock Creek Rd to a vehicle park.
The party then tramped about 20 minutes to reach the platform, built on an elevated area about three years ago.
The platform, anchored to a sheer cliff, overhangs the opening to an underground cavern into which water flows.
Police described the cavern area as sprinkled with large rocks and some undergrowth.
The student party, swollen to 23 with the addition of two DOC staff, approached the platform in two groups.
Eighteen climbed on to the structure; the other five were slightly behind.
The police statement said the group of five did not see the platform collapse but "heard what is described as a loud crash and thump, followed by screams".
"When they got to the top they saw that the platform and everyone on it had crashed to the bottom of the hole," the statement said.
As some of the following group started to scramble down the steep bush-clad slopes to go to the aid of the victims, DOC staff member Shirley Slatter wrote a note about what had happened and appealed for prompt help.
She gave it to a young student, who ran 4km to the nearest house to summon rescue services.
Former rugby league test winger Jack "Nippy" Forrest said the messenger was in deep shock when he arrived at his home.
"He was mighty brave. He tried to phone the police but I had to complete the call," Mr Forrest said.
Helicopters, ambulances and rescue workers poured into the area.
Local helicopter pilot Chris Cowan was one of the first to fly in. He operated a scoop net in the narrow bush-shrouded valley to lift injured from the accident site.
"I lowered the stretcher on about 40 metres of rope and a couple of the survivors climbed in," he said.
He saw others lying motionless on the ground.
Paramedic Tony Beaumont said the four students who survived went "right to the bottom of the ravine with the platform".
"The gully itself was very hard to locate due to dense bush and the steep nature of the terrain," he said. "Another paramedic and I were winched down to the patients at the bottom of the gully."
Mr Beaumont said that when he arrived at the scene, the situation was calm and well-ordered, with police and ambulance staff already there.
Ambulance staff were assessing which patients were dead and which were alive.
"The platform itself was in one piece at the bottom of the gully with a number of deceased persons on and around it," he said.
The four surviving patients were treated and airlifted to Grey Hospital.
West Coast Healthcare chief executive Jane Holden said last night hospital staff were comforting the shocked parents of students killed in the tragedy.
A team of social workers and mental health workers were on hand to counsel grieving parents, Ms Holden said.
"Many people are in shock and we hope to provide support and be available for them to talk to us," she said.
The hospital had been flooded with telephone calls from distressed parents who believed their children might have been involved in the accident.
"We are inviting them to come to Grey Hospital and wait there," she said.
A number of parents with students from outside the area were travelling to Greymouth last night.
Accommodation would be provided for them.
Police said last night they thought the accident happened about 11.30am.
Prime Minister Jim Bolger said in a statement all New Zealanders would experience a "sense of deep shock and great sadness" over the accident.
Acting Minister of Conservation Simon Upton announced a full independent inquiry would be held. This would investigate the design, construction and maintenance of the platform.
DOC director-general Bill Mansfield was on his way to the accident site last night.
DOC deputy director-general Alan Edmonds said he did not know what had caused the platform to collapse.
"We have no idea yet. There will be an inquiry starting and we hope that will reveal what the problem was.""We will be looking closely throughout the country where we have similar facilities and making sure that the standards that we have and cycles we put them through are being closely followed."
Such platforms had standards of inspection and he imagined the one involved in the accident would have been inspected by field staff "every six months or so".
"Our hearts go out - as all New Zealanders' hearts go out - to those affected. It's an awful tragedy," he said.