The horror theme park accident that killed four people at Dreamworld on the Gold Coast was caught on CCTV, police have confirmed as investigations into the tragedy began in earnest.
Gold Coast Inspector Tod Reid said police would remain on site for a significant amount of time to assist in both the investigation and the recovery of the four bodies.
The four victims were on board the Thunder River Rapids ride, which involved six-person circular rafts riding a heavy man-made current.
"There is CCTV footage available and that will be reviewed as part of the investigation," Inspector Reid said.
Inspector Reid said forensic pathologists had examined the victims, two women aged 32 and 42 and two men aged 35 and 38, "in situ" and the Queensland coroner had also examined the scene.
"We have specialist police here engaged with witnesses and those people are being offered support, along with the responding police are being offered appropriate support as well," he said.
Responders would be on the site well into the night, Inspector Reid said, as he expected the "complex" retrieval of the bodies would involve heavy equipment.
"That will take several hours," he said.
Queensland Ambulance Service acting senior operations supervisor Gavin Fuller said two people were ejected from the ride and the other two were caught in the ride.
"They were assessed by Queensland Ambulance personnel and had all sustained injuries that were incompatible with living," he said.
Mr Fuller said responders had been "deeply affected" by what they had seen and would be offered counselling.
Dreamworld chief executive Craig Davidson said the amusement park would not be open on Wednesday.
Later, the Dreamworld website announced the park would be closed "until further notice".
"At this stage, the park is closed and Dreamworld is working closely with police and emergency services and authorities to establish the facts around the incident," Mr Davidson said.
"We are deeply shocked and saddened by this and our hearts and our thoughts go to the families involved and to their loved ones."
Dreamworld visitor Lisa Walker said the Thunder River Rapids ride had broken down earlier in the day.
"It had broken down and we went back a couple of times to this particular ride," she said.
"We were standing on the bridge watching and the water had stopped.
"There was no rapids."
The tragedy occurred about 10 minutes after Ms Walker and her daughter, Kaylah, walked away from the ride.
"We had just got off the ride, maybe five or 10 minutes, and had come over to the water park," Ms Walker said.
"We had just come back and heard all the sirens and things and we saw all the people being ushered out.
"Some were coming out by themselves, some were coming out on their own. Some were coming out crying, cuddling people.
"It was just horrible."
Queensland Premier Annastacia Palaszczuk said police and workplace health and safety were doing a "thorough" investigation and expected that to continue until early Wednesday morning.
"I understand there were many witnesses and I want to thank paramedics and police who were there," she said.
"I have been told the scene was horrific.
"Everyone is in deep shock that this has actually happened at one of our most popular theme parks, our heart goes out to family and victims."
Prime Minister Malcolm Turnbull was in Brisbane on Tuesday when the tragedy occurred.
"Theme parks are a place for family fun and happiness, not tragedy," he said Tuesday evening.
"This is a very, very, sad, tragic event. Our thoughts and prayers are with the families of those who lost their lives.
"This is a very sad day, and we trust there will be a thorough investigation into the causes of this accident over the days to follow."
Gold Coast mayor Tom Tate said his city would assist the loved ones of the victims in any way it could.
"Any help they need, whether or not they need some help to get family or loved ones back to their hometown, things like that," he told Nine News.
"We want to reach out and let them know that Gold Coasters will be doing our best to make sure they are comforted."
Ardent Leisure, the operator of the Dreamworld theme park on the Gold Coast, had its share price fall by as much as 8 per cent following news of a tragedy at the venue.
ASX-listed Ardent owns Dreamworld and the neighbouring WhiteWater World on the Gold Coast.
- Amy Mitchell-Whittington, Jorge Branco, Tony Moore, Cameron Atfield and Carolyn Cummins
