SYDNEY, Oct. 25 (Xinhua) -- Four adults, two females and two males, were killed in an accident at Australia's Dreamworld on the Gold Coast on Tuesday afternoon.

The four unidentified victims had lost their lives after being trapped on the Thunder River Rapids ride, a water-based raft ride using a conveyor belt at about 14:20 local time (AEDT).

Queensland police confirmed that all four adults had been instantly killed in the incident.

Dreamworld has since evacuated all its other patrons and has closed the park until further notice.

A Queensland ambulance spokesman said two of the people had been "ejected" from the ride, while two others were caught inside and stood no chance at all.

They were believe to be aged from 32 to early 40s.

Dreamworld chief executive Craig Davidson confirmed the incident at a media conference in Queensland adding that the park was working closely with authorities to establish the facts around the incident.

"We are deeply shocked and saddened by this," Davidson said.

Gold Coast Mayor Tom Tate issued a statement expressing the community's shock over the news.

"This is a very sad day for our city," Tate said.

"Our thoughts are with the families of those affected and the emergency staff in attendance," he said.

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

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