The panicked voice saying there was a "raft in the conveyor" of the Thunder River Rapids ride was Dreamworld employee Nigel Irwin's first indication something disastrous had happened at the theme park.
Mr Irwin was manning the Gold Coast park's communication hub on October 25, 2016 when he received a call about a medical emergency on the 30-year-old ride.
On Tuesday, he provided an account of his experience to an inquest into the deaths of Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi at the Southport Coroners Court.
The four visitors died when the ride malfunctioned and two rafts collided.
Mr Irwin told the inquest he simply heard a panicked voice say "I've got a raft in the conveyor".
The victims that lost their lives in the Dreamworld tragedy. Source: SBS News
Only when he looked at CCTV footage and saw a raft on its side did Mr Irwin realise something serious had occurred.
When first aid officers told him to call an ambulance and they had at least one person who was unconscious and "turning blue", Mr Irwin was the man to call triple zero.
As he made the call, Mr Irwin upgraded the emergency to a "222 emergency" - the park's most serious emergency code.
"It basically means we have something terrible going on," Mr Irwin said in a statement to police that was shown to the inquest.
Mr Irwin said everyone had acted as swiftly as they could.
"Unfortunately there was just nothing we could do when we got there," he told the inquest.
The inquest also heard from ex-senior ride operator Stephen Buss, who was terminated by Dreamworld after an incident in November 2014 when two rafts containing visitors collided on the ride's conveyor belt.
CCTV footage of the incident was played in the inquest, showing the two rafts colliding and bumping before the conveyor shut down.
Control room operator Nigel Irwin (left) is seen leaving the Magistrates Court at Southport. Source: AAP
No one was harmed in the 2014 incident.
Mr Buss said he'd mistakenly shut down a water pump and the conveyor belt after receiving a "low-air alarm".
"I don't remember a great collision. I believe the rafts touched," Mr Buss told the inquest.
"If they were touching each other that's why I would have stopped the conveyor."
Earlier, the inquest heard an external engineer had issued a certificate saying the ride was "mechanically and structurally safe to use" just days before the tragedy occurred.
Third party engineer Thomas Polley issued the certificate after undertaking the inspection alongside Dreamworld junior engineer Gen Cruz in September 2016.
Mr Cruz told the inquest he was unaware of any risk assessment or safety audits being undertaken on the ride.
Outside the inquest came revelations some former staff plan to take legal action against the park's parent company.
Four former workers intend seeking compensation from Ardent Leisure for the horrific scenes they witnessed when they responded to the tragedy.
Safety officers Shane Green, John Clark and Rebecca Ramsey and engineer Paul Burke have engaged Shine Lawyers to sue the theme park.
Mr Clark, Ms Ramsey and Mr Green are due to appear at the inquest on Wednesday.
