According to the USGS, the centre of the seismic activity was located at a depth of about 20 miles.
There were no immediate reports of any casualties or material damage being sustained as a result of the quake.
READ MORE: Magnitude 6 Quake Strikes Off Australia's Norfolk Island — USGS
According to the Richter scale, earthquakes with a magnitude of 6.0-6.9 are considered strong and can cause moderate damage to even earthquake-resistant structures.
Earlier this month, the USGS reported another strong earthquake in Australia, which occurred northeast of Norfolk Island.