SIDOARJO, Indonesia - Indonesian rescuers were racing on Tuesday to find 38 people feared trapped beneath the rubble of an Islamic boarding school that collapsed in East Java during afternoon prayers, killing three, according to disaster officials.

Three people were confirmed dead and 99 others survived Monday's collapse at the Al Khoziny boarding school in Sidoarjo, a town about 780 km (480 miles) east of Jakarta, according to Mohammad Syafii, head of Indonesia's search and rescue agency.

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Earlier on Tuesday, disaster mitigation agency spokesperson Abdul Muhari said the unstable building collapsed during construction. "This sudden occurrence caused building material to fall on dozens of students and workers," he said.

An excavator and a crane were among the heavy equipment Syafii said searchers were using to shift the rubble.

Nanang Sigit, a local search and rescue official, said 38 people remained missing and authorities would not use heavy equipment for fear of causing the remaining structure to collapse.

Abdul said nearly 80 of the injured were taken to hospital.

Video images from news channel KompasTV showed families of students clustered around a whiteboard looking at a list of survivors.

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The disaster mitigation agency said the building's foundations allegedly could not support the weight of construction on its fourth floor.

Al Khoziny caretaker Abdus Salam Mujib was quoted by state news agency Antara as saying building work had ended before the prayers but said the foundations could not support the construction.