A Twitter user captured the moment the car jumped the track as the five-car coaster came through a 360-degree loop.
Two people have been killed and two more seriously hurt after their roller coaster car derailed at a Mexican amusement park.
The men aged 18 and 21 died on Saturday when the last car of the Quimera coaster at La Feria Chapultepec Magico came away from the track, flipped upside-down, struck a metal support and fell 33 feet to the ground.
Two women riding in the car survived but were taken to hospital in serious condition; six other riders were treated for shock.
Este es el momento exacto en el que descarrilar un juego mecánico en la Feria de Chapultepec. Se reportan al menos dos muertos. pic.twitter.com/347tL5vElj
The fatal accident was caught on camera, when a Twitter user captured the moment the car jumped the track as the five-car coaster came through a 360 loop and into one of its gentler bends.
Witnesses told El Universal that the two riders who were killed hit their heads on the steel support, and that the coaster dragged the flailing car before it finally detached and plunged to the ground.
Pictures of the aftermath show emergency responders tending to the victims, with the area covered in blood.
Horrific news coming out of Mexico City: Quimera at La Feria Chapultepec Magico has derailed killing 2-3 people and injuring others. pic.twitter.com/eLEnskTGb1
Mexican authorities closed the amusement park to carry out an investigation. Preliminary reports indicate a mechanical failure; the accident is being treated as a case of negligent homicide, according to CBS News.
The German-built, 111'-tall, 3,500'-long Quimera features three loops, and hits top speeds of 53mph.
The 22-year-old coaster debuted at a Malaysian amusement park in 1997, before being moved to the UK in 2000, and then the Mexican park in 2007, Mercury News reported.