Three young women died and two other people are in critical condition after suffering cardiorespiratory collapse during a stampede at a big Halloween party in Madrid, first responders told Efe.

Paramedics received a call at 4:05 a.m. Thursday to attend to several people between 18 and 25 years of age who were in respiratory arrest after being crushed, possibly after they fell down and were trampled in a large crowd of partygoers.

Two of the girls were pronounced dead at the nearby first aid station after emergency teams spent more than 30 minutes trying to revive them and a third was dead on arrival at a local hospital.

In all, 50 health care workers attended to the young people.

A flare was "apparently" what startled the crowd and caused the stampede in which the three young people lost their lives, according to what Madrid police told Efe.

An investigation has been opened to determine the circumstances in the case.

The Madrid Arena, with capacity for some 10,000 people, was the site of the "Thriller Music Park" Halloween celebration staged by a company that offered, for a 25-euro (about $32) entry fee, a "gloomy and fun atmosphere achieved thanks to visual and sound effects" by several well-known deejays, according to the Web page announcing the party. EFE