About 40 witnesses have already provided statements to police, however Detective Inspector Mark Thompson appealed for more to come forward on Wednesday to help piece together the ride's fatal malfunction.

Four adults were killed on Tuesday afternoon when their raft on the Thunder River Rapids ride flipped onto a conveyor belt after crashing into a stationary raft in front of them.

Two children, aged 10 and 12, were in the raft and witnessed their mothers die.

On Wednesday afternoon, Detective Inspector Thompson said 30 detectives and a significant number of scientific police were working on the complex case and a major incident base had been set up at Coomera police station.

"As you can imagine this is a long, detailed process," he said.

He called for anyone with eyewitness accounts, mobile phone footage or photos as well as anyone who took a ride on the Thunder River Rapids on Tuesday to come forward.

Dreamworld chief executive Craig Davidson laid a wreath at the scene on Wednesday afternoon, saying the company's immediate focus was on the families of those who died.

"In paying our respects today, I also want to specifically acknowledge the impact of the event on the two children who were involved in this tragedy," he said.

"These children will have our full support into the future."

Six people were on the inflatable raft on Tuesday afternoon that crashed as it neared the end of the route.

As it reached the top of a wooden conveyor belt, it crashed with another raft and flipped over backwards.

Brother and sister Luke Dorsett, 35, and Kate Goodchild, 32, and Mr Dorsett's partner Roozi Araghi, all from Canberra, and Sydney mother Cindy Low died when they were either trapped under the raft or thrown into the water.

Ms Low's 10-year-old son Kieran and Ms Goodchild's 12-year-old daughter were on the raft and witnessed the disaster.

The police investigation will focus on all aspects of the ride's operation including maintenance schedules, machine components and park policies amid claims that the ride was not working properly earlier in the day.

"The Queensland Police Service will be applying all resources necessary to examine every aspect of what's happened here," Assistant Commissioner Brian Codd said on Wednesday morning.

"We owe it to the deceased and their families, we owe it to the community of Queensland to get to the bottom of what caused this, to hold accountable any person that needs to be held accountable for this occurring ... but most particularly ensuring that this can never happen again."