Four people have been killed on a ride at a theme park on Australia's Gold Coast.
Two men and two women died in an accident on the Thunder River Rapids ride at Dreamworld, a park spokesperson said.
A "malfunction" caused two of the victims to be "ejected" and two others to be "caught inside" the ride, Queensland Ambulance spokesperson Gavin Fuller said.
The victims were in their 30s and early 40s, he added.
The theme park at Coomera has been closed and an investigation into the cause of the incident is under way.
Aerial footage showed emergency workers beside one of the ride's six-seat carriages on the conveyor belt close to where people get on and off the ride.
Nine News reporter Carrie-Anne Greenbank told Sky News: "It is certainly chaos down here at the moment.
"Six people were on the raft when it flipped on a conveyor belt.
"Four of them have been trapped underneath and two have managed to jump free."
Water was drained from the attraction in an attempt to save the trapped passengers, the Gold Coast Bulletin reported.
Lia Capes said she was just about to go on the ride when she saw people crying and running out.
"We saw [a] little girl and we believe it was her mum because it was just her and her little sister that was an infant," Ms Capes told ABC News.
"I was speaking to one of the guys and he said it was the raft or the boat thing in front of him, the whole thing flipped and everyone was screaming."
Ms Capes said Dreamworld staff quickly evacuated the area.
"The little girl that was crying, they asked us to take her because we distracted her, she was bawling her eyes out," she said.
"[Then] people that worked here took her and her little sister away."
Another witness told the Gold Coast Bulletin: "My sister and niece were on the ride, they are so traumatised, there is a woman hanging by her foot, crushed from the ride."
The Dreamworld website describes the Thunder River Rapids as a "white water rafting" ride which travels at up to 27mph (45kph).
Visitors as young as two years old are allowed on the ride.
Dreamworld chief executive Craig Davidson said: "We are deeply shocked and saddened by this and our hearts and thoughts go to the families involved and their loved ones."
In a statement, the theme park said it was "working as quickly as possible to establish the facts around the incident".
It added: "Dreamworld's focus and priority is with the families of those involved in this tragedy and will be providing an update to the public as soon as information becomes available."
Australian Prime Minister Malcolm Turnbull said it was a "very, very, sad, tragic event".
He said: "Theme parks are a place for family fun and happiness, not tragedy."
Gold Coast mayor Tom Tate added that it was "a truly sad day for all".