The multi-storey Islamic boarding school in the town of Sidoarjo suddenly gave way on Monday as students were gathered for afternoon prayers, according to local reports.

“Based on student attendance data, 91 people are suspected to be buried under building materials,” national disaster and mitigation agency spokesperson Abdul Muhari said in a statement late Tuesday.

It earlier said three people died and 38 people were still unaccounted for.

Officials said Wednesday they were still trying to confirm the number of missing when asked at a news conference in Sidoarjo.

Rescue teams were focusing on supplying life support to survivors trapped under the rubble, said Emi Freezer, the national search and rescue agency’s head of operations.

They were concentrating on seven areas where signs of life had been detected, he said.

“The main structure has totally collapsed … We prioritised saving victims who were still responsive.”

Dozens of parents waited Wednesday near the collapsed school building as rescue teams searched for survivors under the rubble.