Witnesses have described scenes of people running out screaming and crying from a Dreamworld ride after four people were killed.
Two men and two women, aged from 32 to their early 40s, died after an accident on the Thunder River Rapids ride at the Gold Coast theme park on Tuesday afternoon.
It is believed a conveyor belt malfunction may have forced one of the rafts to flip over.
"My sister and niece were on the ride," one witness told the Courier Mail. "They are so traumatised. There is a woman hanging by her foot, crushed from the ride."
Emergency services vehicles are seen outside the Dreamworld theme park (AAP)
Gavin Fuller of Queensland Ambulance said two people were ejected from the ride, while another two were caught inside the ride.
Witness Leah Capes said she was waiting by the ride's entrance when people came running out.
"The kids and people in there were screaming. It all happened so quickly. There were heaps of people crying. It all happened so fast.
Another man told the newspaper a girl was pulled from the ride just before it flipped.
Premier Annastacia Palaszczuk says the scene was "horrific".
"They are going to send counsellors there as soon as possible to help those people suffering enormous trauma.
"On behalf of all of Queensland I convey our thoughts and prayers to the two females and two males who are no longer with us."
The park is working with emergency services to figure out what went wrong.
"We are deeply shocked and saddened by this and our hearts and thoughts go to the families involved and to their loved ones," Dreamworld CEO Craig Davidson said.