The quake struck at a depth of 35 kilometres (22 miles) off the northwest tip of New Britain island, according to the US Geological Survey, at 6:00 am local time (0130 IST Monday).
The epicentre was 109 kilometres west of the town of Rabaul.
Quakes are common in PNG, which sits on the so-called Pacific "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.