A ride claiming to be the world’s fastest rollercoaster has ground to a halt after several customers reported broken backs or necks.

At least six riders reported fractured bones after going on Japan’s ‘Do-Dodonpa’ rollercoaster in the Fuji-Q Highland Park, a park spokesperson told Vice World News. Four of them reported fractures in their back or neck.

The ride, which goes from 0 to 180 kilometers per hour in 1.56 seconds, has been suspended until further notice.

‘Do-Dodonpa’ was built in 2001, but the park says that there have been so reports of serious injuries including bone fractures until December 2020.

No technical issues with the rollercoaster were found after it was inspected, the park said.

Sansei Technologies, which manufactured the ride, apologized to injured customers but also said it did not know what caused the injuries.

Architecture professor Naoya Miyasato, who studies rollercoaster designs, told Vice that accidents resulting in broken bones are unheard of.

But, he said, the injuries could be caused by people sitting improperly, without making sure their backs are flush against the seat.

According to the Mainichi Shimbun newspaper, one of the riders who reported injury said she may have been sitting forward during her ride.