More than 200 Dreamworld staff returned to an eerily quiet theme park on Monday, but guests won't be walking through the same doors anytime soon.

Dreamworld CEO Craig Davidson addressed the media outside the Gold Coast venue on Monday afternoon, confirmining that business as usual is still a long way off.

"At this point, there is no time frame or decision about re-opening," Mr Davidson said.

"We will not be making a decision at any stage this week."

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Monday marks six days since four people died on the park's Thunder River Rapids ride - Kate Goodchild, Luke Dorsett and Roozi Araghi from Canberra and Sydney-based New Zealand woman Cindy Low.

Mr Davidson said the park won't re-open before funerals have been held for the four victims. He said a "systematic and methodical" three-tier audit of all the park's mechanical rides was the highest priority.

"Dreamworld has commenced an internal review of all park ride operating policies and procedures. This includes specialist engineering reviews of every ride at Dreamworld. In addition to Dreamworld's internal audit, there will be an independent, arms-length mechanical engineering and workplace safety review of every Dreamworld ride.

"Dreamworld has commenced discussions with a number of the world's leading mechanical engineering and workplace safety experts. Dreamworld will provide further updates over the coming days."

Mr Davidson said the third-tier would include working closely with the Queensland Workplace Health and Safety team.

On Friday, Mr Davidson said "no stone will be left unturned".

Police and the Coroner are still working to determine exactly what caused an inflatable raft to tip upside down on the rapids ride on Tuesday.

The raft, containing six people, was travelling along the conveyor belt to the drop-off point when it hit a raft in front and flipped over.

Two children on the raft - Ms Goodchild's daughter Ebony, 12, and Ms Low's son Kieran, 10 - were thrown from the ride.

The four others did not survive.

A memorial day was originally planned for Friday, with entry costs to be donated to the Red Cross. But on Thursday afternoon Dreamworld released a statement cancelling the public event.

"Dreamworld has been advised by Queensland Police Services that we are unable to proceed with tomorrow's memorial service as planned," the park said in a statement.

"Obviously the integrity of the Coronial Investigation is of paramount importance and postponing the service will give QPS the time it needs to conduct this investigation.

"We will provide an update to the media on Monday with regard to the memorial service and re-opening of the Park."

A candlelight vigil was held on Friday night and staff returned at their own discretion, on Monday morning.

"Returning to work is not compulsory - it is for those staff who want to come back and help the park and support their colleagues," Mr Davidson said.