A tsunami warning was issued for PNG and the neighbouring Solomon Islands but later cancelled by the Hawaii-based Pacific Tsunami Warning Center.
Sunday morning's aftershock, estimated as 6.1-magnitude by the US Geological Survey, occurred 96 kilometres from Panguna at a depth of 18 kilometres.
Seismologists at the Port Moresby Geophysical Observatory said they were the latest in a series of "fairly big" shocks in the Panguna region, including sizeable 7.6 and 7.5-magnitude tremors on April 11 that had killed at least two people -- an elderly woman and separately a four-year-old boy who suffered fatal head injuries when his house collapsed according to local media reports.
"There were a couple of deaths, two maybe, and there was damage to some semi-permanent bush houses and other buildings," an observatory spokesman told AFP.
Schools, health facilities and water infrastructure had also been damaged by last week's major earthquakes, displacing 50 families, according to The National newspaper.
The spokesman said officials in Port Moresby had been so far unable to reach remote and isolated Bougainville to check whether there had been casualties or damage from Saturday night's quake.
Earthquakes 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.
Last year in February the remote town of Lata in the Solomons was hit by a devastating tsunami after an 8.0-magnitude earthquake. The tsunami left at least 10 people dead, destroyed hundreds of homes and left thousands of people homeless.