The quake's epicentre was around 90 kilometres (55 miles) south of Porgera in Enga province, according to USGS, and hit at a depth of 35 kilometres.
USGS said some casualties and damage were possible and recent earthquakes in the area had caused tsunamis and landslides.
It said homes in the region were "a mix of vulnerable and earthquake resistant construction".
Earthquakes 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.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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