A 6.8 magnitude earthquake hit Papua New Guinea on Friday, 106 kilometres (66 miles) south-southwest of the town of Kokopo, the US Geological Survey said, just a day after a 6.7 magnitude tremor in the region.

The quake hit at 0806 GMT, 693 kilometres northeast of the Pacific nation's capital Port Moresby, in the New Britain region at a depth of 57 kilometres.

The USGS had initially reported the earthquake's magnitude at 7.1 with a depth of 53 kilometres, but later revised its strength and distance from PNG.

There were no tsunami warnings, the Pacific Tsunami Warning Center said.

A 6.7 magnitude quake hit the same region on Thursday, 131 kilometres southwest of Kokopo, but there were no reports of serious damage.

"This is the second earthquake that has occurred in that region over the last two days," co-director of the Joint Australian Tsunami Warning Centre Daniel Jaksa told AFP.

"The previous one was about 10 kilometres to the southeast of this particular epicentre. It's a very uninhabited region off the island of New Britain.

"The earthquake was a measure of 7.1, so that's about 30 times smaller than the (recent) earthquake in Nepal.

"It should be like the one yesterday -- no real impact."

New Britain, the largest island of the Bismarck Archipelago, is east of mainland New Guinea and has a population of around 500,000 people.

The island lies on the 4,000-kilometre long Pacific Australia plate, which forms part of the "Ring of Fire," a hotspot for seismic activity due to friction between tectonic plates.

Jaksa said earthquakes of similar magnitudes that occur within 24 hours were not common, and cautioned there was a possibility the tremors could be foreshocks ahead of a bigger seismic event.

"The probabilities of another earthquake in that region actually increases with an event like this, but it's... one of the most active earthquake zones in the world," he said.

"Unfortunately this is completely unpredictable. Certainly the potential is there for a larger event to occur but a lot of the time, it doesn't."