Four people have died at an amusement park in Australia after an accident on a water ride on Tuesday.

The victims were all adults — two men and two women — Stuart Cohen reports for NPR from Sydney. The accident occurred at Dreamworld amusement park, a popular destination on Queensland state's Gold Coast.

"Witnesses say the circular raft the people were in flipped over near the start of the ride," Cohen reports. "Authorities say they're still investigating the circumstances of the accident, but confirmed two people were thrown from the ride, while two more were trapped inside."

The ride, called "Thunder River Rapids," wasn't an extreme, adventure-seeking sort of thrill: Visitors say it's one of the milder rides at Dreamworld, Cohen reports.

The Associated Press writes that the ride was open to children as young as 2.

Queensland police Officer Tod Reid told the AP that police were working to determine what went wrong:

"Reid said he was not aware of any previous problems with the ride. Police were interviewing witnesses and reviewing closed-circuit television footage of the incident while crews worked to remove the bodies from the scene on Tuesday night, he said.

" 'It is a complex retrieval involving heavy equipment and that will take several hours,' Reid said."

Dreamworld CEO Craig Davidson said the company was "deeply shocked and saddened," the AP reports.

Summer, peak tourist season in Australia, begins in just a few weeks.

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