A tsunami warning was issued for Papua New Guinea and Solomon Islands, the Hawaii-based Pacific Tsunami Warning Center said, adding that it was "not known that a tsunami was generated".
The quake struck at a depth of 30 kilometres just before 11:30 pm (1330 GMT), USGS said. It reported another 5.6-magnitude quake had happened around 20 minutes later in the same area at a depth of 69 kilometres.
A 6.6-magnitude quake occurred in the same area on Saturday morning, USGS reported earlier.
Quakes of such magnitude 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.