The quake struck at 3:39am local time at a depth of 15 kilometres about 20 kilometres offshore of the New Ireland town of Taron, the US Geological Survey said.
A spokesman for the Port Moresby-based National Disaster Management Office said there were no immediate reports of damage but regional disaster management teams would carry out assessments later in the day.
"We've been in contact with the regional office and they are going out to check it," he told AFP.
The epicentre was more than 800 kilometres east of the 7.5-magnitude quake that hit the highlands region of the Pacific nation on February 26, killing at least 67 people.
PNG sits on the so-called Pacific Ring of Fire, a hotspot for seismic activity.
Its mountainous and remote terrain means it often takes several days for information about damage from quakes to reach officials and aid agencies.
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