The quake hit at a depth of 10 kilometres (6.2 miles) about 116 kilometres from the nearest city of Panguna on Bougainville Island, at 11.22am local time, the United States Geological Survey said.
There were two aftershocks in the Bougainville region measuring 5.2 and 5.0 magnitude respectively.
“Any tsunami generated is going to be very local… and about half-a-metre in size,” Mark Leonard, a senior seismologist for the government agency Geoscience Australia, told AFP.
“And as they propagate away from their source, they weaken fairly quickly.”
Separate data collected by Geoscience Australia had the initial quake at 6.7 magnitude and at a depth of one kilometre.
Leonard said the south-west area of Bougainville, which is the closest land mass to the quake zone, was not known to be heavily populated.
There were no immediate reports of damage.
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.
The last tremor off the Pacific nation’s coast was a 6.4-magnitude quake that struck in the New Britain region in early November.
In 2013 the neighbouring Solomon Islands were hit by a devastating tsunami after an 8.0-magnitude earthquake rattled the region. That tsunami left at least 10 people dead, destroyed hundreds of homes and left thousands of people homeless. (AFP)