THE investigation into what went wrong in this week’s Dreamworld tragedy is “growing in complexity”, police say, as the theme park’s operators today revealed Workplace Health and Safety Officers are on site at the theme park.

Dreamworld CEO Craig Davidson, who attended a candlelight vigil at Dreamworld on Friday night, used a media update to reassure Dreamworld staff will be fully paid while the park remains closed in the wake of the four deaths on the Thunder River Rapids ride.

“Our hearts and thoughts are still with the families affected by this tragedy. We are continuing to

co-operate with the authorities throughout the ongoing investigation,” he said.

While Dreamworld will not reopen before funerals for the four have been held, “from next week there will be a gradual process of inviting people back to work at the Park if they wish to return,” he said, adding “this is not compulsory”.

“There are still many things to do at the Park for staff such as feeding animals, gardening, and cleaning,” he said in the statement.

Four people lost their lives after a raft on the Thunder River Rapids flipped backwards after two of the seats came together, causing one to flip back, on Tuesday.

The victims were Canberrans Kate Goodchild, Luke Dorsett and Roozi Araghi, and Sydney-based New Zealand woman Cindy Low.

Dreamworld won’t reopen before funerals have been held for the four.

Two children: 10-year-old Kieran Low and 12-year-old Ebony Goodchild, who were thrown clear and escaped physically uninjured.

Theme park management is also working to ensure no customer would be out of pocket, with refunds on pre-purchased tickets and extensions of partial refunds for season passes, Mr Davidson said.

He thanked organisers of the official GIVIT fund set up for families and community members directly affected by Tuesday’s tragedy.

Meanwhile a fund set up to assist the partner and two children of park victim Kate Goodchild has topped $48,000.

Long-time family friend Sandra Brookfield started an online funding page for the Goodchilds with the approval of Kate’s mother Kim Dorset. Mid-afternoon on Saturday, the mycause.com.au fund had reached $48.200. “We are looking at a date later next week for Luke and Kate’s funeral,” Ms Brookfield said.

As investigations into the grim tragedy continue, Mr Davidson confirmed Workplace Health and Safety Queensland Officers “are on site from today and we are giving them every support they need. They have full access to the Park.”

Earlier, without going into detail, Queensland Police Commissioner Ian Stewart said the investigation “brought in a range of specialist investigators, from other agencies that need to be engaged”.

Mr Stewart said “the investigation at Dreamworld will take time” but did not elaborate on a time frame.

Patience in regard to Dreamworld and Moorooka bus incident will be exhibited in investigative process. @CoPStewart — QPS Media Unit (@QPSmedia) October 28, 2016

Thank you for coming in. We rarely had a week when such tragedy has occurred. We will not cut corners. @CoPStewart — QPS Media Unit (@QPSmedia) October 28, 2016

The officer confirmed a thorough investigation is being initiated under the direction of the coroner, under which specialist engineers will examine policy and the procedures of the ride, its maintenance schedules and how the ride is made up.

He said the CCTV footage will be a “very important part of the investigation”, adding that criminal aspects including negligence will be addressed if warranted.

“The Queensland police service will be applying all resources necessary to examine every aspect of what’s happened here,” he said.

“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, and to hold accountable any person that needs to be held accountable if that’s the case, but most particularly ensuring this can never happen again.”

He stressed these investigations will take time, saying thoroughness was more important than speed.

The union representing Dreamworld staff says it raised grave concerns about safety at the park 18 months ago, but its owner fought efforts to obtain information.

The Australian Workers Union says it went to Dreamworld’s owner, Ardent, and to the state regulator to express grave concerns, including about the safety and operation of equipment.

Queensland Secretary Ben Swan said the union even put in a right-to-information request with the division of Workplace Health and Safety, but Ardent opposed it.

Mr Swan said the union took its concerns about general safety directly to Ardent as far back as April 2015.

“We have had concerns about maintenance and operations regimes,” Mr Swan told ABC radio on Wednesday, declining to provide details.

“I can’t speak to the particular ride in question. What I can say is it is now a matter of public record because we put a right to information request into the Commission of Workplace Health and Safety that we have concerns.

“We’ve expressed those concerns directly to the company. I don’t want to inflame the situation because I think people’s priority should rightly be on taking care of the situation that immediately exists but we did hold some very grave concerns about safety of equipment and the operation of equipment at that site.”