A chlorine gas leak disrupted a furry convention at a hotel in a suburban Chicago neighborhood.

The gas permeated various floors of the building late at night, prompting an evacuation. Police believe it was a deliberate attack.

The alleged attack happened at around 12:40 a.m. Sunday morning at the Hyatt hotel in Rosemont, a suburb of Chicago, according to the Chicago Tribune. The leak began at the ninth floor of the hotel, spreading throughout the floor. The incident interrupted the MidWest FurFest convention, which was being held at the hotel.

Emergency responders transported 19 people to local hospitals after reporting nausea, dizziness and other medical problems. People evacuated the hotel, staying outside or going to the nearby Donald E. Stephens Convention Center.

The main event happening at the hotel was the FurFest convention, in which people "come together to celebrate furry fandom, that is, art, literature, and performance based around anthropomorphic animals," according to the event's website.

Many of the convention's attendees were dressed in animal costumes and stood outside in the cold as hazardous materials technicians decontaminated the area. By 4:20 a.m. the building was deemed safe and people began returning. Officials say they found powdered chlorine, which they believe to be the source of the gas.

The event, which brought people from all over the country and world, had to be temporarily suspended but resumed when attendees were able to return.

"We ask you to continue to be patient, and remember that the volunteers who make Midwest FurFest happen intend to give 110 percent to make sure that the fun, friendship, and good times ... overshadow last night's unfortunate incident," the group said in a statement, according to the Associated Press.

Police are investigating the incident as a criminal act. They say the gas was released intentionally.