It was sunny Tuesday when two women and two men boarded a large circular raft at Dreamworld, Australia's largest theme park, and headed for the raging waters of the Thunder River Rapids Ride.
It's one of the park's most popular attractions, a fast moving "foamy water track" that pushes riders through turbulent, artificial rapids at up to 45 km per hour - equivalent to about 30 mph, according to Australian Broadcasting.
Still, children are allowed to climb aboard. It's considered tame, a family ride.
But Tuesday, at around 2 p.m., authorities say the ride malfunctioned during the foursome's trip.
Two people from the raft were ejected; the other two were trapped inside.
News of the fatal tragedy spread rapidly across the country, prompting fans of the theme park and Thunder River Rapids ride to share messages of disbelief on social media. Queensland Mayor Tom Tate said the incident marked a "very sad day for our city." The prime minister offered prayers for family of the dead.
"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 CEO Craig Davidson said at a press conference hours after the tragedy.
Authorities would not say what type of injuries the four people suffered, only that they were "incompatible with life."
Police Inspector Tod Reid said at a press conference that victims were two females, ages 42 and 32, and two males, ages 38 and 35. Their names have not been released to the public. Authorities are still working to confirm their identities and notify family members.
Dreamworld is located on what's called Australia's Gold Coast, a 60-minute drive from Brisbane on the country's east coast in Queensland.
Information from authorities did not paint a clear picture of what exactly happened in the moments leading up to the "malfunction." They would not say if those trapped in the ride were under water or caught up in the mechanism itself during the press conference, though an initial news alert from Queensland police indicated the victims were injured by the conveyor belt.
Queensland Ambulance spokesman Gavin Fuller did say that while emergency services were en route to the disturbing scene, Dreamworld staff gave the victims first aid but were unable to save their lives.
"It is one of the most tame rides here and certainly one for the families," Lisa Walker, a New Zealander visiting from New Guinea, told the Guardian.
She was one of hundreds of people Tuesday who was asked to leave the amusement park over the loud speaker as word of the incident rippled throughout the crowds.
One man who witnessed the incident told the Gold Coast Bulletin that he saw the ride flip at the tail end of its circuit and that just before it overturned, a girl was pulled from the ride.
Other witnesses said people ran from the Rapid River ride, screaming.
"There were heaps of people crying," Leah Capes told the Bulletin. "It all happened so fast."
Water from the ride was drained amid efforts to save the victims, the Bulletin reported.
As guests left the park, they were asked to report to guest services and speak with police if they witnessed the tragedy.
The park closed at 3:30 p.m., according to the Bulletin.
At the press conference Tuesday afternoon, Fuller told reporters the rescue efforts were traumatizing for first responders.
"A number of the staff that were here today have been deeply affected by what occurred," he said.
Multiple agencies were on scene throughout the afternoon, including a forensic team, workplace health and safety and the coroner.
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