Three young women were crushed to death in a stampede at a Halloween celebration in Madrid apparently sparked when a partygoer threw a firework, police said Thursday.

"Three victims were trampled to death and two others were injured," a police spokesman told AFP.

The disaster struck some time before 4 am at an indoor stadium that can accommodate thousands of people and had been transformed into a party venue for Halloween.

The victims were aged between 18 and 25, police said.

The deadly crush was apparently triggered when someone inside the stadium hurled a firework, the spokesman said, adding that the site had been evacuated and an investigation launched.