A stampede in an arena where thousands of people were attending a Halloween dance party killed three women and critically injured two others early Thursday, officials said.
It happened just after 4 a.m. in a passageway within the venue leading to the central concert area at Madrid Arena, where the disco-style party with American DJ Steve Aoki was under way.
Someone set off a flare or a firework, causing the stampede that trampled the five young women, Deputy Mayor Miguel Angel Villanueva said.
One witness said the stampede left partygoers piled atop one another as high as her shoulders.
"I saw a mass of people . screaming 'Help, get me out of here,' with security guards tugging at them," Ana Gomez told state broadcaster TVE. "I remember seeing the face of one young man, and his expression was that of sheer terror."
Thousands of people were attending the party when the stampede occurred, leaving the victims with trauma injuries or breathing and heart failure, emergency services spokesman Fernando Prado said.
Villanueva said the venue's maximum capacity of 10,600 people had not been exceeded and that authorities decided not to evacuate the arena when the accident occurred. Most partygoers were not aware of the stampede because it was confined to the passage, he said.
Aoki said he was "devastated" to hear about the deaths and cancelled a planned show in the northern city of Bilbao on Thursday night "out of respect for those who lost their lives and those who are injured."
He said "the safety of my fans has always been my top priority and had I known that there was any distress putting people in jeopardy within the venue I would have ended my show immediately."
Halloween has recently become a popular festivity in Spain, coinciding with the traditional feast of All Saints.
In Germany, 19 people were crushed to death in a stampede and 342 others were injured two years ago at a techno party in Duisburg.