JOIN USThe US Geological Survey said the quake occurred at a depth of 45 kilometres, 103 kilometres east of the mountain city of Lae and 326 kilometres north of the capital Port Moresby.
Geoscience Australia, which measured the quake at 6.5 magnitude, said it was so close to the coast it was unable to say whether the epicentre was under sea or land.
"People very close to it would have got a very, very strong shake, and there's a possibility of damage there right in that vicinity," seismologist David Jepsen told AFP.
"And then there's the township of Lae, about 100 kilometres to the west of that event, and there's the possibility there could be some light damage in that major township."
But he said that level of quake was common in that region.
Papua New Guinea, mired in poverty despite rich mineral deposits, sits on the so-called "Pacific Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.
A giant tsunami in 1998, caused by an undersea earthquake or a landslide, killed more than 2,000 people near Aitape, on the country's northwest coast.