An investigation has been launched into how eight people became trapped upside down on a rollercoaster at a festival in the US.

Some of them were trapped for more than three hours at the event in Wisconsin.

The rollercoaster’s cars got stuck near the top of a loop at the Crandon International Offroad Raceway.

Rescue workers arrived to find eight passengers hanging upside down from their safety harnesses.

Firefighters used ladder trucks to reach them, securing each one before releasing their over-the-shoulder safety bars, the Crandon Fire Department said.

It took nearly three-and-a-half hours to get all the passengers down. One person was taken to a hospital.

According to the fire department, a ride operator said something broke down mechanically on the rollercoaster, which had been inspected by the state.

The state Department of Safety and Professional Services is responsible for reviewing plans for amusement parks and inspecting rides in Wisconsin.

Spokesman John Beard said that the agency is investigating and dispatched an inspector to the scene.