There were no immediate reports of casualties or damage from the shallow quake close to the coast, around 100 miles (162 km) southwest of Rabaul.
The Pacific Tsunami Warning Centre (PTWC) issued a threat warning for the country's coastline located within 300 km of the quake's epicentre.
"Government agencies responsible for threatened coastal areas should take action to inform and instruct any coastal populations at risk," the PTWC said in its alert. "Persons located in threatened coastal areas should stay alert for information."
Australian authorities said there was no threat to the Australian coastline from the quake, which was initially reported as a magnitude 7.2.
(Reporting by Jane Wardell and Alison Bevege in SYDNEY. Additional reporting Sandra Maler in Washington; Editing by James Dalgleish and Tom Brown)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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