At least 91 students remain trapped in concrete rubble almost two days after an Islamic school building collapsed on them, authorities said after reviewing attendance records and reports from anxious families of those missing.

More than 300 rescue workers desperately worked to free survivors Wednesday morning, after the structure fell on top of hundreds of people, mostly teen boys, who had been performing afternoon prayers Monday in a prayer hall at a century-old al Khoziny Islamic boarding school in East Java province that was undergoing an unauthorised expansion.