Twenty-one were killed and over 50 injured early Monday morning at a South Side Chicago nightclub with an established record of building code violations in one of the most deadly stampedes in recent history.

A team from the University hospital helped administer medical attention at the scene and treated eight patients at the clinic, said John Easton, director of public affairs for the hospital.

According to Easton, half of the patients came between 4:00 and 4:30 a.m. and the other half later in the morning. None were seriously injured.

“One of the patients I spoke with was just at the coat check when people started to flood out,” Easton said. “He came in for pulled muscles, bumps and bruises.”

The melee began shortly after 2 a.m. when a fight broke out between two clubgoers inside the South Side club E2, 2347 South Michigan Avenue.

To quell the fighting a security guard used pepper spray or mace, sparking a stampede inside the packed club, with a crowd estimated between 1500 and 2000, according to witness reports.

Early in their inquiry, the fire and police departments–both of which are investigating the incident–cited locked doors as the chief cause of death.

According to fire commissioner James Joyce, firefighters responding to a call to the dance club–the second floor of the Epitome restaurant–encountered several locked doors. They used sledgehammers and metal bars to pry open the doors to help free people.

“The owner knows damn well that he is not to open that second floor facility,” Joyce told reporters Monday afternoon. “We found doors locked, we found doors blocked by storage and in some cases what appeared to be bags of laundry,” he said. “Those are violations.”

Nicole Aughtry, 30, recalled her experience at the club to the Chicago Tribune.

“The whole time I was in there, I felt a bad vibe,” she said, adding that it was particularly crowded because of President’s Day. “And I knew something was going to break out. You couldn’t breathe, you couldn’t dance.”

When the fight began, Aughtry rushed for the stairs, she said, and was carried with the crowd.

To make it out of the club, she had to step on people.

“I was trying to stay up,” she said. “I was holding onto the banister with both hands because I saw once you went down, you couldn’t get back up.”

A majority of the fatalities occurred near the front of the club at its only door. When authorities arrived, they found 19 in cardiac arrest.

In a press conference, Terry Hillard, superintendent of Chicago police, said that detectives are in the process of determining exactly what was sprayed and by whom, noting that since 2000, police have investigated 80 incidents in the vicinity of the club.

“We are interviewing and seeking out any witnesses that could help us determine exactly what happened inside this club this particular night,” he said. “We also are retrieving, reviewing, and attempting to download high-tech video from the establishment.”

The Chicago Police Department declined further comment while the investigation is still pending.