Police in Chicago are investigating why 21 people were crushed to death and many more injured in a stampede at a nightclub.

Panic broke out when Mace, or pepper spray, was released on the upper floor of the two-storey Epitome club on the city's South Side.

"The owner knows damn well that he was not to open that second-floor facility James Joyce Fire Commissioner

Clubbers were trampled as people rushed for the exits.

Many could not get out because some doors were locked or blocked with obstacles, police say.

The spray was used by club security officers to break up a fight among a group of young women, according to reports.

City officials say a judge ordered the owners to close the club last July because of safety violations - including failure to provide enough exits.

"The owner knows damn well that he was not to open that second-floor facility," Fire Commissioner James Joyce said.

City officials say they plan to go to court to seek criminal contempt charges.

However a lawyer for the owners said they were still challenging the court order telling the club to shut down.

He also said that security guards whose spray set off the stampede worked for a promoter, not the club.

Left for dead

The E2 club above the Epitome restaurant had been packed ahead of the Presidents' Day public holiday on Monday.

Many of the injured suffered breathing problems

Mr Joyce estimated that about 500 had been inside the club - earlier, the fire department had put the number at 1,500.

Clubbers rushed down a staircase to try to get out when the spray was released.

As some fell, others simply poured on top of them.

One man told local television he was knocked unconscious and left for dead.

"The last thing I remember is getting hit by a guy who must have weighed 300 pounds, and the next thing I know I woke up in a body bag."

The incident has proved one of the worst of its kind in the United States.

In December 1979, 11 people were killed in Cincinnati in a crush to get into a concert by British rock group The Who.

In December 1991, nine people were crushed to death in a gymnasium stairwell while awaiting a celebrity basketball game at New York's City College.

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Read a selection of your comments on this subject below.

I wasn't at E2 the night of this tragedy, but I have been there before and even then it was so crowded that I decided to leave and go elsewhere. My friend was at E2 on Sunday, and luckily I spoke to her this afternoon - she is doing alright - very shaken up, but that is expected. It's unfortunate though that when she left home Sunday evening with two of her friends to have a good time, and take a break from work that she would be arriving to E2 with two people who she will never see again! My deepest sympathy goes to all those who lost someone.
Debra, USA

I was by the wall with my girl and noticed a crowd of people coming towards us. My girl hit the ground and I tried to get to her but it was too late. Although I was trampled on I got out in time but now I feel bad that my baby had been left behind.
Devin Smith, USA

People couldn't breathe Dejuan, USA

I was in the club. Everything was fine until a fight occurred and security sprayed pepper spray. People couldn't breathe, so they started toward the stairwell. I can estimate about 200 or more rushed to the stairwell. The stairwell is like a cliff - if one falls, then all are going to fall. Of the 21 who are dead, I knew 5 people that died.
Dejuan, USA

I would first like to send my condolences to all the families who lost a loved one in this tragic event. I would also say that I have been to the club on three different occasions. I know that the stairs are a danger - only one way in and one way out. The last time I went which was the Sunday before Labor Day last year and a girl got murdered. The security was so disorganized people in the lines were pushing and jamming the doors to get in. That was the last time I went to E2 and I will never be back again and I hope their doors never open again.
Renee Williams, United States

I was there, although downstairs, people made comments like, nerve gas, please get out the way, anthrax, please get out the way, terrorist please get out the way and we just jumped on each other so fast you can't believe it
James, USA

I was at the club, the people were scared because someone said it was a terrorist gas attack.
Brad James, USA

Not an eyewitness but I've been there. The club is actually called E2 - it's above a restaurant called Epitome.
Michael, USA