Four die on Dreamworld ride

Four people have died after an accident on a family ride at Australia's biggest theme park, Dreamworld.

The victims, two men and two women, became trapped on a conveyor belt at the Gold Coast theme park after their raft flipped on the Thunder River Rapids ride about 2pm (local time) on Tuesday.

Two people were thrown clear, while the other two were stuck in the ride itself.

Queensland Ambulance senior operating officer Gavin Fuller said all four suffered fatal injuries and could not be revived despite several crews attending the scene.

Mr Fuller said the ride suffered a malfunction which caused the accident.

It's unconfirmed whether the four victims are related, with police refusing to reveal their identities until next of kin have been contacted. Their ages range from 32 to early 40s, Mr Fuller told reporters.

Dreamworld chief executive Craig Davidson said the thoughts of the park were with the families and loved ones of those killed.

"We're all deeply shocked and saddened by this. We will work closely with police and emergency authorities in this matter."

Owners Ardent Leisure announced the park would be closed on Wednesday.

Gold Coast mayor Tom Tate issued a statement expressing the community's shock at the incident.

"This is a very sad day for our city. Our thoughts are with the families of those affected - and the emergency staff in attendance."

Thousands of shocked patrons flooded from the park after it was closed in the aftermath of the accident.

A coronial investigation into the cause of the accident and the deaths is under way, with workplace health and safety officers and police forensic crash investigators visiting the scene.

Mr Fuller said first-response paramedics were deeply affected by the scene and were being counselled.

The Thunder River Rapids Ride is Australia's only river rapids ride and opened in December 1986.

Dreamworld's Rocky Hollow Log Ride was shut down in April this year when a man fell from the ride and nearly drowned.

Witness Lia Capes told the ABC she was just about to go on the ride when she saw people running out, crying.

"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.

Tuesday's tragedy ranks among the world's deadliest theme park accidents.

Earlier incidents include eight teenagers killed in a 1984 fire at the Six Flags Great Adventure amusement park in New Jersey in the United States; six people killed by a failed simulated rocket launch in Shenzhen, China, in 2010 and five children killed when the Battersea Park Big Dipper malfunctioned in Britain in 1972. 

- AAP and Reuters