I am an Australian PhD student. Most of my fellow students do not have a Masters.
My university lists the requirements for a PhD here
Of particular note:
1.1.4 To be eligible to apply for entry to a Doctoral program, an applicant must demonstrate the capacity to undertake research at the Doctoral level by the attainment of at least one of the following:
(i) A Bachelor’s degree with at least Second Class, Division A (Honours) in a degree program that included a total of at least a semester of supervised project work, the results of which contributed to the Honours grade;
(ii) A postgraduate qualification which included: (a) supervised research component(s) of at least one semester or equivalent and resulted in the production of output(s) graded at the equivalent of Distinction or better, and (b) at least one research methods subject;
(iii) A Research Masters degree, where at least two thirds of the degree consisted of a supervised research component and resulted in the production of a thesis or equivalent;
(iv) Enrolment at this or another Australian university in a higher degree by research for the equivalent of at least 0.5 EFTSL with demonstrated satisfactory performance in the supervised research component(s);
(v) A combination of qualifications, research training and experience, considered equivalent to the above by the Responsible Academic Officer in the Enrolling Organisational Unit, e.g., senior authorship of at least one peer-reviewed publication plus completion of an appropriate research methods subject.
Most of the time people who get in appear to have either first class honours or some published research. I have seen domestic students with a lower GPA work with a supervisor to publish some research in order to be accepted into the PhD.