Two children remain under observation at CWM Hospital after suffering electrical flash burns during the incident.
The children, aged 6 and 13, are receiving medical treatment following the incident on Wednesday afternoon.
The Ministry of Employment, Productivity and Workplace Relations has launched an Occupational Health and Safety investigation to determine the cause of the electrical fault and the circumstances surrounding the incident.
The Ministry says preliminary findings indicate that an electrical fault occurred inside the building's ground-floor main switchboard room at about 3.20pm.
Employment Minister Agni Deo Singh says some electrical components in the switchboard were found to have sustained heat damage.
However, the exact cause of the fault remains under investigation.
The affected switchboard has been shut down, with access restricted to authorised repair and inspection personnel.
The Ministry says electricity should not be restored until the electrical system has been fully inspected and cleared by the relevant authorities.
Singh says the safety of workers, visitors and members of the public must always come first.
