JAKARTA -- The death toll from the collapse of a school building in Indonesia's East Java province has risen to 20, a local rescue official said Saturday.

Currently, over 40 people remain missing, and the death toll is expected to rise.

Part of the multi-storey Al Khoziny Islamic Boarding School in Sidoarjo district caved in on Monday during unauthorized renovation, leaving dozens of students trapped.

"The excavation is not easy as rescuers need to lift the debris, cut the frames, and then retrieve the bodies from the pile of materials," said Nanang Sigit, head of the East Java Search and Rescue Office.

Rescuers deployed heavy machinery on Thursday after no further signs of life were detected. Earlier, they had relied mainly on manual excavation out of concern that heavy equipment could cause further collapse.