Indonesian rescue workers were racing against the clock on Wednesday in the search for survivors from a school collapse in the province of East Java, with at least 91 students still unaccounted for, along with three confirmed dead and about 100 injured. 

The Islamic boarding school, which authorities said was undergoing an unauthorised expansion to add two new stories, collapsed during afternoon prayers on Monday, sending slabs of concrete and other heavy debris crashing onto the students below.

Most rescues typically happen within 24 hours after such a disaster, with chances of survival decreasing each day after that, and more than 300 workers continued to work desperately at the scene to try and reach those who have been detected to be still alive and trapped below. 

"We hope that we can complete this operation soon," Mohammad Syafii, head of Indonesia's National Search and Rescue Agency, said. 

"We are currently racing against time because it is possible that we can still save the lives of those we have detected within the golden hours," he said at the news conference.