SIDOARJO, Indonesia (AP) -- The bodies of three boys were pulled early Friday from beneath the rubble of a school that collapsed in Indonesia and with more than 50 students still unaccounted for the death toll was expected to rise, authorities said.

Rescue crews had been working by hand since the collapse of the school Monday as they searched for survivors, but with no more signs of life detected by Thursday they turned to heavy excavators equipped with jackhammers to help them progress more rapidly.

The structure fell on top of hundreds of people in a prayer hall at the century-old al Khoziny Islamic boarding school in Sidoarjo on the eastern side of Indonesia's Java island.

The students were mostly boys in grades seven to 12, between the ages of 12 and 19. Female students were praying in another part of the building and managed to escape, survivors said.

Eight students have been confirmed dead and about 105 injured, many with head injuries and broken bones, and 55 remain unaccounted for.

Two of the bodies found Friday were in the prayer hall area and one was found closer to an exit as if he had been attempting to escape, according to Suharyanto, the head of Indonesia's National Disaster Mitigation Agency, who goes by one name as is common in Indonesia.

Authorities have said the building was two stories, but two more levels were being added without a permit. Police said the old building's foundation apparently was unable to support two floors of concrete and collapsed during the pouring process.

School officials have not yet commented.

Crews worked in the hot sun Friday to break up and remove large slabs of concrete, with the smell of decomposing bodies a grim reminder of what they would find underneath.

Suharyanto told reporters at the scene that the recovery efforts were expected to be complete by the end of Saturday.

Indonesian crews pull 3 bodies from rubble of collapsed school with more than 50 boys still missing