SIDOARJO, Indonesia (AP) — A building under construction at an Islamic boarding school in Indonesia collapsed on dozens of praying students Monday, killing at least one, injuring dozens and burying others in the rubble.

Police, soldiers and rescue workers dug into the debris through the night to locate additional students and pulled out eight weak and injured survivors more than eight hours after the collapse at Al Khoziny Islamic Boarding School in the East Java town of Sidoarjo. Rescuers also said they saw additional bodies, indicating the death toll was likely to rise.

The students had been performing afternoon prayers in a building that was undergoing an unauthorized expansion when it suddenly collapsed on top of them, provincial police spokesperson Jules Abraham Abast said.

One male student was killed and 99 other students were injured and taken to hospitals, some of them in critical condition, officials said.

Most of the victims were male, because female students were praying separately in another part of the building and managed to escape, survivors said. Residents, teachers and administrators assisted injured students, many with head injuries and broken bones.

Authorities launched an investigation into the cause of the building’s collapse.

Abast said the old prayer hall was originally only two stories, but had been renovated by adding two more floors without a permit to build a new structure.

“The old building’s foundation was apparently unable to support two floors of concrete and collapsed during the pouring process,” Abast said.

Television reports showed dozens of rescue workers, police and soldiers desperately digging through steel reinforced concrete debris in search of survivors in overnight rescue operations, supported by heavy equipment.

Families of the students gathered at hospitals or near the collapsed building, anxiously awaiting news of their children. Relatives wailed as they watched rescuers pull a dusty, injured student from a buried hall.

Heavy slabs of concrete and other rubble and unstable parts of the building hampered search and rescue efforts, said Nanang Sigit, who led the effort.

“We have been running oxygen and water to those still trapped under the debris and keeping them alive while we work hard to get them out,” Sigit said. He added that rescuers saw several bodies scattered under the rubble, but that they focused on saving those who were still alive.

Several hundreds of rescuers, including self-contained breathing apparatus equipped with extrication, medical evacuation and other rescue operation support equipment, continue to search in a non-stop operation under the rubble of devastated building for bodies, and whenever possible survivors.