The quake struck in the Solomon Sea at a depth of seven kilometers (4.3 miles) at 2:38 am (Sunday 1638 GMT), with its epicenter 70 kilometers southeast of Kandrian and 470 kilometers northeast of Port Moresby, the USGS said.
Authorities did not raise tsunami warning along the nation's coast lines. No casualties or major damages has been reported so far.
Papua New Guinea has experienced a series of powerful earthquakes this year.
Last July, a 7.3 magnitude quake rocked the New Britain region following a number of lesser magnitude temblors that hit the country early this year.
Papua New Guinea is part of the Pacific Ocean's "ring of fire," where earthquakes of this magnitude usually occur.