It was supposed to be gigantic Michael Jackson ‘Thriller’ themed party to celebrate Halloween in the Spanish capital.

But the fun turned to tragedy when three young women were killed in a stampede as partygoers attempted to leave the Madrid Arena.

Witnesses say the panic began after a flare was thrown into the crowd. Others described a scene of chaos, with lots of screaming and some people fainting.

“There was a staircase. Then all of a sudden there was a rush of people and some of them stumbled; and there was a crush,” described one man who attended the party.

Another man said: “They did not say anything about the stampede inside the club. There was a moment when the music stopped, but nothing else. They didn’t announce that something had happened.”

A third man who was inside the arena was also unaware of the tragedy: “We didn’t notice anything. The party continued as normal and when the music stopped, people left at around 6.00 am which is the normal thing for a party.”

Local media said the three victims were aged between 18 and 25.

Two other woman are in a critical condition in hospital.

An investigation has begun to determine whether the 12,000 capacity venue was overcrowded.