The deaths of four people on Dreamworld's Thunder River Rapids ride on the Gold Coast could have been avoided with the press of an emergency button, a coronial inquest has heard.

Key points: The rapids ride was reset by engineers after breaking down twice in hours before fatal incident

The rapids ride was reset by engineers after breaking down twice in hours before fatal incident A young ride operator didn't know there was an emergency stop button within reach

A young ride operator didn't know there was an emergency stop button within reach The same operator had to signal to control room to stop the ride, costing crucial seconds

Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi were killed instantly from crushing injuries when their six-person raft collided with an empty vessel and flipped backwards in 2016.

Two children, who were also on board the same raft, managed to escape.

Detective Sergeant Nicola Brown told the court a young female ride operator had access to an emergency button, which could stop the ride within two seconds, but she told police she was not aware what the switch really did.

Investigators told the inquest that the ride staff had 57 seconds to identify a raft was trapped on a conveyor belt before a second raft, carrying the victims, hit it and flipped.

Forensic crash investigator Steven Cornish told the inquiry that pressing the emergency button would have changed the outcome.

Steven Whybrow, the barrister for Kate Goodchild and Luke Dorsett, asked Mr Cornish, "How long through that process could that pressing have been delayed, but still avoided this tragedy?"

"... right up until the point of contact," Mr Cornish replied.

"Similarly, if there was an emergency stop at the main panel that functioned the same way … and it had been pressed … that would have also avoided this tragedy?"

"Yes," Mr Cornish responded.

Police said the deaths could have been prevented if an automatic system had been put in place to stop the ride when water levels dropped too far. ( AAP: Dan Peled )

'Nobody uses the emergency stop button'

Detective Sergeant Brown said the emergency stop button at the unload area was designed to halt the conveyor within two seconds.

During cross-examination, Mr Whybrow said the emergency button was not clearly labelled.

"She was told not to worry about that button, no-one uses it?" Mr Whybrow asked.

"Yes," Detective Sergeant Brown replied.

The court heard a memo was sent to employees about a week prior to the deaths, telling staff to only use the button if the "main control panel cannot be reached".

Mr Whybrow said in the email, Dreamworld was "dissuading people from pressing that button".

Detective Sergeant Brown said staff had raised concerns that the buttons to stop the rides were confusing.

"It is a confusing control panel and that has been raised by the auditors," she said.

Detective Sergeant Brown said two operators managed the ride from a main control panel at another location which only had a "slow" stop button.

"It's not an emergency stop, it's a slow stop. It takes approximately seven seconds," she said.

Detective Sergeant Brown said the young ride operator closest to the incident had to signal to an operator at the control room, which cost crucial seconds.

The inquest also heard there was no drill training for staff at Dreamworld to determine how they would react in an emergency situation.

Roozbeh Araghi, Luke Dorsett, Kate Goodchild, and Cindy Low lost their lives at Dreamworld in 2016. ( Facebook )

Ride failed twice within hours of fatal accident

Detective Sergeant Brown told the inquest a large pump on the Thunder River Rapids ride had failed at both 11:50am and 1:09pm without any incidents.

"Engineering attended, reset the pumps and operating continued as per normal," she said.

Queensland Emergency service personnel at the Thunder River Rapids ride. ( AAP: Dan Peled )

Previous incidents January 2001 — Collision of rafts due to operator error

January 2001 — Collision of rafts due to operator error October 2004 — A visitor fell into the water while unloading when rafts bumped together

October 2004 — A visitor fell into the water while unloading when rafts bumped together August 2005 — Three rafts mounted up together at the same time

August 2005 — Three rafts mounted up together at the same time 19 October 2016 — Water pump failed but nobody hurt

19 October 2016 — Water pump failed but nobody hurt 25 October 2016 — Two water pumps failed at 11:50am and 1:09pm

25 October 2016 — Two water pumps failed at 11:50am and 1:09pm 25 October 2016 — Fatal incident at 2:00pm when pump failed and two rafts collided on conveyor

In his opening address to the inquest, counsel assisting the inquiry Ken Fleming QC described the tragedy as "a significant mechanical breakdown".

The coroner heard that in 2001 one of the ride's rafts flipped during the 'dry run' at the start of the day and no-one was on board.

Mr Fleming said the 2001 incident was so serious it prompted a staff member at the time to write in an email: "I shudder when I think if there had been guests on the ride."

He said past incidents and previous breakdowns of the ride would be explored and investigated during the inquest.

No automatic switch to shut down ride if water dropped

Mr Fleming told the inquest the fatalities in 2016 happened on "what was one of, if not the most, popular ride built as suitable and safe for the whole family".

"The south pump failed causing a massive drop in the water," he said.

"As the water dropped, one boat became caught on rails."

The ride was modified in1980s and 90s and the number of long slats on the conveyor belt was reduced, leaving a gap which allowed a raft to get caught and flip.

Floral tributes outside Dreamworld for the four victims of the ride malfunction in 2016. ( ABC News: Ashleigh Stevenson - file photo )

Answering questions from Mr Fleming, Detective Sergeant Brown said there was no switch to automatically shut down the Thunder River Rapids if water levels dropped too much.

Mr Fleming: "Was there any device fitted anywhere that would monitor the water levels that you could see?" Detective Sergeant Brown: "No." Mr Fleming: "Was there any device which could automatically switch the whole of the ride off if water levels dropped?" Detective Sergeant Brown: "No." Mr Fleming: "The only way it could be done is by operator intervention?" Detective Sergeant Brown: "That's right."

The court heard the victims were "forcibly propelled", hitting the stationary raft.

The court heard the Forensic Crash Unit used test dummies to try and replicate the fatal incident.

Senior Constable Steven Cornish said investigators repeated the process more than 20 times.

He was asked by counsel assisting the inquiry Ken Fleming QC if the fatal incident was eventually replicated.

"Not entirely, no," he replied.

Senior Constable Cornish said there was a "high level" of noise surrounding the operation of the Thunder River Rapids ride due to the large water pumps, moving conveyor, crowd chatter and noise from the nearby Buzz Saw ride.

Mr Fleming told the inquest the Dreamworld tragedy "has been felt Australia-wide".

He told the coroners court issues "gravely emotional" to the families of those killed would be explored at the inquest.

"It will be difficult for them throughout the inquiry," he said.

He said 37 witnesses would be called to give evidence at the inquest over two weeks.