At least 91 people remain trapped under building rubble following a school collapse in Indonesia, government authorities said.

Indonesia’s National Agency for Disaster Management, or BNPB, reported the latest figures on Tuesday evening, revising the number from an estimate of 38 people earlier in the day.

The agency said at least six people are still alive under the rubble, where they have been trapped for nearly two days.

“Rescue efforts are currently being carried out manually by digging holes and openings to evacuate survivors,” BNPB said in a statement on Facebook, noting the use of heavy equipment could trigger further collapse.

“The joint [search and rescue] team has detected signs of six people still alive in one section of the collapse. Through existing gaps, rescuers have managed to deliver food and water to sustain the victims,” the agency said.

Officially, the number of deaths from the school collapse stands at three and nearly 100 injuries, although the figures do not count people still trapped.

Of those injured, 70 have been discharged, and 26 remain in hospital, the agency said.

More than 300 rescue workers from BNPB, the military, and national police have been dispatched to the scene of the accident at Al Khoziny Islamic Boarding School in Sidoarjo, East Java, which collapsed on Monday afternoon while students – mostly teenage boys – and staff were attending prayers.

“If the assessment concludes there are no more survivors, the next phase will involve the use of heavy equipment to recover deceased victims still trapped,” the agency said.

Authorities say the school’s foundational pillars gave way while unauthorised construction work was under way on a higher floor.