At least 54 people were injured in an explosion at a mosque within a school complex in Indonesia’s capital Jakarta on Friday, according to local police.

Jakarta North Police Chief Asep Edi Suheri said the blast took place around 12:30 pm (0530 GMT) at State Senior High School 72 (SMA Negeri 72). “The initial data we have received indicates that there are approximately 54 individuals affected. Some have minor injuries, some moderate, and some have already been discharged,” Asep told reporters.

He said the cause of the explosion is still under investigation, adding that initial inspections suggest several possible scenarios — including an electrical short circuit, a malfunctioning electronic device, or a homemade explosive.

Footage aired on local media showed members of a special police unit deployed at the school. Several of the injured were taken to nearby hospitals for treatment, according to media reports.