Teams from Papua New Guinea's National Disaster Centre are at the quake's epicenter near Chambri Lakes, a remote and swampy part of East Sepik province, Reuters quoted Felix Taranu, a seismologist with the Port Moresby Geophysical Observatory, as saying.
Four people are confirmed dead and 300 houses destroyed along the Sepik River region, and there are unconfirmed reports of further deaths and several hundred more houses destroyed, he added.
"The local member is liaising with his people to confirm the exact details of the number of houses and victims and any effects in the region," Taranu said.
The quake struck at a depth of 80km (49.71 miles) early on Monday, according to the European Mediterranean Seismological Centre (EMSC).
Papua New Guinea straddles the Pacific's "Ring of Fire", a region known for frequent earthquakes. A 7.6 magnitude quake last September killed seven and triggered landslides across three provinces.
MP/PR