Yes. I wouldn't recommend it. As different as the MS and PhD are, doing an MS will be more like a PhD than anything else a person will have experienced during their undergraduate years.
Edit. Australian degrees are about half way in between the UK and US system. Most candidates take around 4 years.
In the UK at my institution, there was only optional teaching load for PhDs, you knew you had funding for 3 years before you started and there weren't many taught courses, so you can dive straight into research.
The only people I know who finished their PhD in 3 years were exceptionally good (not to mention lucky in their research) and wanted to move on for other reasons, such as leaving the country with a partner for a postdoc job.