Denise O’Toole was teaching her 28 students at 2:28 p.m. on Monday in a fifth-floor classroom in Chengdu, Sichuan province, China, when the building she was in began to sway and plaster and dust started to crumble and fall.

O’Toole, a former Cony High School teacher, and her students were experiencing the impact of an earthquake that measured 7.9 on the Richter scale. On Wednesday, Chinese government estimates pegged the death toll at 15,000 and counting. Thousands more, largely in remote areas, were reported missing and trapped.