Three young children and one man were killed on Wednesday in a horrific car fire that was declared a crime scene by the police in the northeastern Australian city of Brisbane.

Detective Inspector Mark Thompson of the Brisbane police said a woman who was also involved in the deadly blaze was in the hospital with critical injuries. He told reporters Wednesday that the three children and the two adults were all “known to each other.”

The investigation was still in its infancy, he said, adding that the family members of those killed still needed to be notified. “Therefore it would be inappropriate for me to go into the detail of how these people know each other,” he said.

All three children were under the age of 10, he said.

The morning blaze in the quiet streets of the suburb of Camp Hill shook residents, with some recounting in news reports that they had tried to extinguish the fire but were beaten back by its ferocity.