Four people were killed on Tuesday on a river rapids ride at Australia's biggest theme park, police said.

The incident took place at Dreamworld, in the Gold Coast tourist district of northeastern Queensland state, police said on their official account on social network Twitter.

Shares in park owner and operator, Ardent Leisure Group, dropped 7 percent in the final hour of trade after the incident, having spent most of the day little changed.

"Dreamworld is working as quickly as possible to establish the facts around the incident," theme park officials said in a statement.

Police said they responded to reports of several people injured by a conveyor belt on the Thunder River Rapids Ride. The four dead were adults, they added, but gave no details ahead of a scheduled news conference.

"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," the Dreamworld statement said.