By Agence France-Presse
The quake struck at a depth of 10 kilometres (6.2 miles) some 195 kilometres west of the town of Mount Hagen, the US Geological Survey said.
Much of the Pacific nation is mountainous and remote, meaning it often takes days for information about damage from natural disasters to reach officials and aid agencies.
The country's rugged highlands region was hit by a 7.5-magnitude quake on February 26 that buried homes and triggered landslides, killing at least 125 people.
There are regular earthquakes in Papua New Guinea, which sits on the so-called Pacific Ring of Fire -- a hotspot for seismic activity due to friction between tectonic plates.