When a gunshot rang out at Debsirin Nonthaburi School on the outskirts of Bangkok on Friday morning, 14-year-old Khim and her classmates leaned over a balcony, wondering whether the noise had come from a nearby construction site.

Then more shots rang out.

A teacher quickly ushered the students into a classroom, checked a messaging group and confirmed their worst fears: An active shooter was inside the school.

“I heard multiple gunshots and felt like we weren’t going to survive,” Khim, who asked to be identified only by her nickname, told Reuters on Saturday.

She described how her classmates pushed desks against the classroom door, switched off the lights and huddled near the windows as they waited in fear.