Visitors to M&D's amusement park in Motherwell, Scotland, took to social media starting around 4 p.m. local time after a carriage on the park's Tsunami roller coaster derailed.
"(I) literally got off the Tsunami at M&D's and then (I was) walking past and the next lot of people get on, and the full thing goes off the tracks," Katie Burns wrote on Facebook. "Honestly never been so scared in my life. … Kids and adults are still on it, upside down. It's like something out of a horror film, children crying and everything."
Literally got off the Tusami at m&ds and then walking past and the next lot of people get on and the full thing goes off...Posted by Katie Burns on Sunday, June 26, 2016
Demi Campbell said she was "in complete shock" after watching the derailment.
A spokesperson for the theme park said in a statement that M&D's was closed Sunday afternoon.
"A serious incident occurred at M&D's today involving the Tsunami roller coaster," the statement said. "We have all emergency services on site to assist."
According to M&D's, the Tsunami is Scotland's only inverted roller coaster. It reaches speeds of up to 65kmph (40 mph).
It's not the first time emergency response teams have been called to the park. In March, eight people had to be rescued after the Tornado roller coaster became stuck. A mechanical failure in July 2011 trapped nine people on the Tsunami roller coaster for hours.