The death toll from an Indonesian school collapse rose to 63 on Monday, officials said, as workers pulled more remains from the rubble of the building that collapsed last week.

Part of the multi-storey Islamic boarding school on Indonesia’s Java island collapsed as more than 150 students gathered for afternoon prayers.

Around half a dozen youngsters are still unaccounted for.

“We hope we can conclude the recovery today (Monday), and we will return the bodies [to the families],” National Search and Rescue Agency (Basarnas) operations director Yudhi Bramantyo told a press conference on Monday.

The collapse was Indonesia’s deadliest disaster so far this year, Budi Irawan, the deputy head of the national disaster agency (BNPB), said.

Investigators have been examining the cause of the collapse, but initial indications suggest that substandard construction may have contributed to the incident, according to experts.

The families of the missing agreed last Thursday for heavy equipment to be used, after the 72-hour “golden period” for the best chance of survival came to an end.

Lax construction standards have raised widespread concerns about building safety in Indonesia.

At least three people were killed and dozens were injured in September when a building hosting a prayer recital collapsed in West Java.