Three of these people suffered severe injuries when an empty concrete-slab building being used for fire simulation rescue practice suddenly erupted in an explosion, sending glass shards and other shrapnel into a crowd of onlookers, police reported.
The group of people had gathered some 50 metres away to watch the fire.
Two adults, a four-year-old and eight children between 10 and 14-years-old were treated in a nearby hospital after sustaining cuts and bruises from the debris.
Most of the injured were allowed to return to their homes after treatment, but three remained for observation overnight.
A car parked nearby the accident was also damaged, police said, adding that they have undertaken an investigation into the incident.