Nineteen people were hospitalized early Sunday after an intentional chlorine leak at the Hyatt Regency O’Hare during the 2014 Midwest FurFest, public safety officials said.

The leak, reported at about 12:45 a.m. Sunday, caused a complete evacuation of the hotel at 9300 W. Bryn Mawr Avenue. The hotel was hosting the Midwest FurFest convention. Attendees dress up like furry animals and celebrate art, literature and performance based on anthropomorphic animals, according to the convention’s website.

Rosemont Public Safety received several calls from guests at the hotel stating there was a noxious odor spreading across the 9th floor, according to the statement. More people told units upon arrival that the odor was also on the 8th floor.

Crews discovered a high level of chlorine gas in the air and evacuated hotel staff and guests, the statement said. Several neighboring fire departments assisted at the scene, the statement said.

The source of the gas, which appeared to be powdered chlorine, was found in the 9th floor stairwell, the statement said. HazMat technicians decontaminated the area and conducted tests.

Guests were temporarily kept at nearby Donald E. Stephens Convention Center. They were allowed to return once the hotel was deemed safe, the statement said.

Paramedics took 19 guests who complained of nausea and dizziness to hospitals, the statement said.