Roads are reported to have cracked and buildings destroyed in the quake, which occurred nearly seven kilometers from the town of Kainantu in the north-east of the country.
At least three people have died in subsequent landslides and several more are said to be seriously injured.
However, due to the remote geographical locations of the hardest-hit villages along the Finisterre mountain range, the extent of the damage is still unclear.
- It was like sitting on an ocean - everything floated, says a resident of the coastal town of Madang.