It's understood the victim, thought to be aged in her 20s, was rushed to hospital in a critical condition but died in care.
Police were called to a home in North Toowoomba shortly before 2pm following reports of a shooting and found the woman on the footpath.
A vehicle of interest had been located and three associates of the dead woman were being questioned as witnesses, Acting Inspector Brian Collins told reporters on Wednesday afternoon.
Asked whether they were of interest to the investigation, he said: "They're with police and assisting police with their inquiries.
"It's extremely alarming," Insp Collins said about when and where the incident happened.
"We're talking about early afternoon, about school pick-up time ... and the police response in ascertaining what happened will be swift."
Investigators are calling on anyone in the West and Christmas streets area after 1pm who may have witnessed what happened or is able to share dashcam footage to come forward.
According to local media, the dead woman suffered multiple gunshot wounds.
A middle-aged man also suffered serious injuries and a second man was treated for emotional distress.
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