A boat on a thrill ride at an amusement park that bills itself as the best in the world accidentally rolled backward down a hill and flipped over in water when the ride malfunctioned Friday, injuring all seven people on it.

Operators stopped the Shoot the Rapids water ride after the accident, which occurred on the ride's first hill, the Cedar Point amusement park said. Park police officers, medical technicians, ride operators, and park visitors waded into the water and helped the passengers off the boat.

Cedar Point officials wouldn't say how the boat landed after rolling downhill. But witnesses told the Sandusky Register newspaper the boat flipped on its side or upside down.

Matthew Orr, of Euclid, was at the park and said people were belted into the boat and were trapped.

"We jumped in and helped them get out," he told the newspaper. "If we didn't help, I don't even know what would have happened."

In a 911 recording, the caller says she was on the ride when it capsized. "Some people are still in the water," she tells the dispatcher.

Cedar Point officials said six of the seven boat passengers on the log flume were evaluated and treated at the park and then were released and the other was taken to a hospital for further evaluation before being released.

Cedar Point, which says it has been rated the best amusement park in the world for 15 years in a row, is in Sandusky, along Lake Erie between Cleveland and Toledo. It's owned by Cedar Fair Entertainment Co.

The Shoot the Rapids ride, rated an Aggressive Thrill, "takes you up and splashes you down," Cedar Point says on its website.

"Shoot the Rapids feels like a real wild river adventure with canyons, a tunnel and something unexpected around every corner!" it says.

The accident was being investigated by Cedar Point officials, who said they had reported it to state officials. They said the ride, which opened in 2010, will stay closed until park and state inspectors complete their review.

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"The safety of our guests is our number one priority," Cedar Point said in an emailed statement.

In another amusement park accident on Friday, a woman riding a roller coaster at a Six Flags amusement park in Arlington, Texas, died, and witnesses say she fell from a ride that is billed as the tallest steel-hybrid roller coaster in the world. The Texas Giant reaches 14 stories high and has a drop of 79 degrees and a bank of 95 degrees.