VH-IGJ departed Canberra CTA on the Canberra Yass track 20 miles from Canberra and cruising at 4500 ft. Approximately five minutes later VH-IJA departed Canberra CTA on the same track, 20 miles from Canberra and cruising at 6000 ft. At that time the controller noted a radar return two miles ahead of IJA, orbitting on the Canberra Yass track, also at 6000 ft but climbing. Flight Service was advised so as traffic could be passed to IJA and Flight Service was also asked to contact IGJ. The pilot of IGJ reported to Flight Service at 6700 ft. The base of CTA was 6000 ft at that position. The radar return was identified as IGJ. Shortly afterwards IGJ left CTA no descent. Factors The pilot of VH-IGJ initiated a climb into controlled airspace without a clearance.