By Helen Regan, CNN(CNN) — Indonesian rescue teams are frantically searching for scores of young students buried for two days under concrete rubble after their Islamic boarding school collapsed on them during afternoon prayers. But in total, at least 91 people remain missing, feared under the rubble, Indonesia’s National Disaster Management Authority (BPBD) said late Tuesday. Holy Abdullah Arif, 49, ran to the school when he heard about the collapse to find that his 13-year-old nephew was listed among the missing. Construction work was being carried out at the prayer hall at the time of the collapse, BPBD spokesperson Abdul Muhari said in a statement Tuesday. The prayer hall construction had been ongoing without a permit, the AP reported, citing local authorities.