The quake struck at a depth of 33km at 11.30am GMT on Saturday, the US Geological Survey said.
There were no immediate reports of damage or injuries after the earthquake hit an area 186 km east of the western province of Kandrian.
It comes after Papua New Guinea was struck by a 7.5 magnitude quake which claimed the lives of more than 150 people last year.
The country’s strongest earthquake on record triggered landslides, which buried houses, contaminated water sources and destroyed crops.
At least 170 aftershocks were recorded following the incident, according to the World Health Organisation.
Earthquakes are common in Papua New Guinea, which sits on the Pacific's "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.
Its mountainous terrain means it often takes aid agencies and government officials days before they can gather information on damage and casualties.
New Britain island has a population of nearly half a million people.
Additional reporting by Reuters
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