Emergency responders on Saturday night rushed to the scene of a Quinceañera in San Francisco, where 19 people, including at least 10 children, were sickened after eating a candy that contained an unknown substance, according to the San Francisco Fire Department.

All 19 were hospitalized, including three children who were sent to an intensive care unit and remained there Sunday. Other victims were in "moderate condition," fire officials said.

Police ruled out a HazMat situation, and sources said that it seemed as if a " watermelon candy substance" could be to blame.

Security guard Raul Hernandez called 911 as people started to become violently ill.

"It was just one after another and another," Hernandez said. "A gentleman was holding his chest. The young lady, she couldn’t talk and was gasping for air."

The birthday celebration was being held at the Women's Building on 18th Street near Valencia Street, where several community and social service events are held.

People taken to the hospital reported heart palipitations, rashes and shortness of breath, according to officials. One woman leaving the building told NBC Bay Area that those who got sick had a foamy-type substance coming from their mouth.

"Preliminarily, it appears this is a candy substance, but that has to be vetted and verified," said Jonathan Baxter of the San Francisco Fire Department.

San Francisco's Public Health Department was interviewing those who fell ill and conducting lab tests on the food and candy at the center of the investigation.

"Could this have been a willful act to harm people at this party? We don’t know but we’re investigating that," said police Sgt. Michael Andraychak. "So far, however, we’ve found nothing to indicate that this was an intentional act."

Anyone who knows anything or has any symptoms is asked to call the police.