A national day of mourning has begun in Liberia after a fire broke out at a religious boarding school, claiming the lives of 27 children.

The children were sleeping in a building attached to a mosque right before it caught fire on Tuesday evening around 11 pm local time, Presidential Press Secretary Isaac Solo Kelgbeh told CNN.

“It is saddening even when a single citizen dies; what much more about 28 children, potential leaders, who were aspiring for a better and prosperous future,” Liberia’s President George Weah said.

The president added on Twitter:

“My prayers go out to the families of the children that died last night in Paynesville City; as a result of a deadly fire that engulfed their school building. This is a tough time for the families of the victims and all of Liberia. Deepest condolences go out to the bereaved.”

Police spokesperson Moses Carter told Reuters that the fire was caused by an electrical problem but an investigation is underway.

The fire is believed to have broken out while the school students were sleeping. The children, some as young as 10, were not able to escape the building because there was no fire exit and security steel bars on the window.

Two teachers are also among those who perished in the fire. Two survivors were taken to a local hospital and remain in critical condition.

The victims were buried on Wednesday in line with Islamic funeral rites, which states that a person must be buried as soon as possible after they die, which is typically within 24 hours.