Dreamworld ride operator didn't know about emergency button that could've prevented tragedy.

A Dreamworld ride operator was unsure which emergency button to press to prevent the Thunder River Rapids ride tragedy, an inquest has heard.

The principal police investigator has told a packed Southport Coroners Court the main control panel for the ride was confusing and the operator had previously been deterred from using an immediate shut down button.

On the opening day of the inquest into the October 25, 2016 tragedy which killed four people, the court also heard of a history of malfunctions on the Thunder River Rapids.

Detective Sergeant Nicola Brown said the water pump on the supposed family-friendly ride at the Gold Coast theme park stopped working twice in the hours before the fatal incident.

Det Sgt Brown said no engineering staff attended the second time, and that it was simply reset.

Less than an hour later, the pump stopped working a third time, resulting in the water level near the unloading point of the ride to drop so rafts were no longer buoyant but were sitting on maintenance rails.

A raft carrying six guests collided with an empty raft that was stuck on the rails, raising both into a vertical position.

Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi all died when they were thrown from the raft into the conveyor belt mechanism.

Det Sgt Brown said multiple safety recommendations such as the inclusion of an emergency stop button on the main control panel and the installation of CCTV footage for the unloading area operator were not implemented.

The inquest heard there were no sensors or guides on the ride for operators to determine when water levels had dropped to a dangerous point.

Det Sgt Brown said there had been a window of 57 seconds between the empty raft getting stuck on the conveyor and the collision which led to the tragedy.

She said the main control panel for the ride was "confusing" and a ride operator at the time of the incident "wasn't sure which button to press" under the stress of the situation.

An emergency button at the unloading dock could have stopped the rafts from moving along the conveyor in two seconds, Det Sgt Brown said.

However, a memo had been sent to Dreamworld staff days before the tragedy warning the emergency stop button was not to be pressed unless there were certain specific circumstances.

Det Sgt Brown said the ride operator had been told "don't worry about that button, no-one uses it".

Ms Goodchild's 12-year-old daughter and Ms Low's 10-year-old son survived the incident despite also being thrown out of the raft.

Counsel assisting Ken Fleming QC said the tragedy had been "felt Australia-wide", and the main aim of the inquest was to prevent any similar tragedies from happening again.

Among the relatives of the victims in the gallery are Ms Low's husband Matthew and Ms Goodchild's husband Dave Turner.

Dreamworld suffered steep falls in visitor numbers following the fatal accident and the park's subsequent 45-day shutdown.

The inquest continues.