What to Know The Joker's Jinx stopped mid-ride, stranding 24 people 80 feet in the air, at an angle.

Some riders initially thought it was a joke. Their parents waited on the ground, not knowing if their children were safe.

Six Flags said the ride "did not complete its regular ride cycle, causing it to stop at a safe location on the track."

Twenty-four people riding a roller coaster were stuck in midair for more than three hours when the ride froze Thursday evening at Six Flags America in Prince George's County, Maryland.

The Joker's Jinx roller coaster stopped at the amusement park about 6 p.m., stranding riders as young as 6 years old at an angle, 80 feet in the air at a 30-degree angle.

Firefighters used a hydraulic crane to remove passengers from the ride one by one, finishing the rescue in the dark after 9 p.m.

When the ride stopped, some riders initially thought it was a joke. Helpless parents waiting on the ground for their children, not knowing if they were safe.

Alarming video shot from Chopper4 showed a first responder standing on a rail of the roller coaster, harnessed for safety.

All riders are OK, Prince George’s County Fire Department spokesman Mark Brady said. Some riders waved to Chopper4 as it hovered over the area.

Julia Valverde, 15, and her younger brother were on the ride when it froze. She hesitated about riding the coaster.

“To me, it's always seemed like the scariest ride,” she said. “I was kind of stalling it the whole day. I was like, ‘Let’s do something else beforehand,’ because it always terrified me.”

News4’s Jim Handly shows how firefighters rescued dozens of people stuck 100 feet in the air on a roller coaster at Six Flags America in Prince George’s County, Maryland.

When the roller coaster started to lose momentum, Julia and her brother thought it was a joke, fitting with the ride’s theme.

“We thought it was going to start shooting off again,” she said. “After a good 30 seconds, the realization hit that no, we were really stuck.”

The children's parents were on the ground waiting for their kids when they realized they were stuck in midair.

“You’re worried for them because you can’t go save them,” Javier Valverde said. “If there was a ladder, I would have gone up the ladder if I could.”

Valverde said he felt "very, very thankful" when firefighters rescued his children.

Other parents said the scare left them nervous.

"My kids were just on that ride," Renee Clingerman said. "I thought that could have been me."

Six Flags issued a statement Thursday evening, saying, "Joker’s Jinx did not complete its regular ride cycle causing it to stop at a safe location on the track. The Prince George's County Fire Department is on site to assist in getting the riders safely off the ride. The safety of our guests is our highest priority and the ride will be closed for a thorough inspection before re-opening."

The ride was last inspected on March 3 with no violations outstanding, a representative for the Maryland Department of Labor, Licensing and Regulation said.

The Joker's Jinx is the same ride on which two dozen people were trapped in August 2014. On that hot day, riders were given umbrellas by rescue crews to shade them from the sun during the rescue, which took four hours.

Introduced in 1999, the Joker’s Jinx accelerates from 0 to 60 mph in about 3 seconds, according to the theme park’s website. Constructed in a “spaghetti bowl” design, the ride takes 1 minute 15 seconds to complete.

The ride has this memorable tagline: “The Joker is laughing with you, not at you.”

An estimated 1,500 people were hurt on amusement park rides in America in 2015, according to the National Safety Council.