WASHINGTON, Feb 17: At least 21 people were killed and 19 others critically injured in Chicago early Monday when hundreds of panicked nightclub patrons rushed down a stairwell and were crushed, police said. “There was a disturbance ... in which pepper spray or Mace may have been used — some sort of stampede occurred,” said a police officer.

People, already on their edge because of a high security alert, tried to escape in panic, causing the tragedy, police said.

Last week, the Bush administration ordered a high security alert across the United States following reports from American intelligence agencies that terrorists may target public places to prevent a possible US military offensive against Iraq.

There were more than 1,500 people in the two-story Epitome Night Club on Chicago’s Southside when the incident occurred after 2am, Fire Commander Will Knight said.

“It appears a disturbance from within led to a mass chaos where people headed for the door. Most of the fatalities appear to have been crushed or had injuries due to suffocation,” said a police officer.

At least 21 people were confirmed dead, a Chicago police spokesman said. In December 1991, nine young people were crushed to death in a gymnasium stairwell while awaiting a celebrity basketball game in New York.