At least 11 people died after the roof of a gymnasium collapsed during a women’s volleyball practice in China on July 23, officials said.

The incident happened Sunday in a school gymnasium in Heilongjiang province, CNN report. The newspaper said 19 people, including 17 girls and two coaches, were at the gym for practice. Authorities have not released the ages of the victims, but local media said the parents were 15 and 16, respectively.

A school gymnasium roof collapsed in northeastern China, killing 11 people in suspected illegal activities by construction workers working on a nearby building, state media said, citing initial investigations. https://t.co/Y1Ni9SWY7A

— Caixin Global (@caixin) July 24, 2023

Preliminary investigations indicated that the collapse may have been caused by construction materials left by construction workers working on nearby buildings, CNN reports. According to the media, recent rains have weighed the material perlite, which likely led to the collapse. (Related: Roof collapse near Ohio State University, 14 injured)

The victim’s parents are reportedly angry at the authorities’ handling of the tragic incident. “We were told that our daughter was gone, but we never got to see her. All the children had mud and blood on their faces when they were sent to the hospital. I begged them to let me know their identity. What if it wasn’t mine?” according to guardian.

Local officials said the collapse had highlighted certain problems, including “insufficient investigation of potential safety hazards” and “inadequate safety oversight,” according to a CNN report. The tragedy prompted officials to vow to adhere more closely to the national security campaign, known as the 2023 Special Action Plan, and move forward, according to the newspaper.

Officials will “reflect deeply, learn lessons, and comprehensively and thoroughly implement the 2023 Special Action Plan to investigate and remediate serious safety hazards,” CNN reported.